Few actors draw us back like John Cusack – we can't get enough of that humble, sincere, over-articulate character he plays so well. So, Carole Cadwalladr asks the star of Say Anything and High Fidelity, why all the psychopaths?

Yesterday he was in Australia. Or was it tomorrow? John Cusack is confused. He's just returned from the Gold Coast, where he was filming his latest movie – Hard Drive, a heist thriller – and there's a brief interlude before he heads off again. Somewhere in between he saw the so-called "super moon", last week's fuller-than-normal full moon, but where?

"I was flying all day, so I saw it the second day," he says. "I was in the future, then I had to fly back to the past because I was a day ahead. It was day in Australia and then I flew all the way back, and it was daylight the entire time so I was sort of on the other side."

It's not an entirely coherent explanation, this, even from someone in the full throes of jet lag, and yet it sounds uncannily familiar: the rambling, over-articulating John Cusack of his early hit Say Anything, or his mid-career hit Being John Malkovich; the John Cusack which reached its natural apotheosis as Rob Gordon, the bumbling boy-man of High Fidelity, the Nick Hornby adaptation which Cusack himself co-wrote and produced.

In part it's the voice– which his sister, the comic actress Joan Cusack, shares – and I wonder aloud whether it owes its debt to Chicago, where they both grew up, or Cusackness?

"Chicago is more of a flat 'a'," he says. "I don't think we have that…" And he trails off, leaving Cusackness in the frame.

But then it's a quality that his fans, particularly women of a certain age who first came across him nearly 30 years ago as lovelorn Lloyd Dobler, the hero of Say Anything, will recognise instantly – a hang-dog odd-man-outness which accompanies expectations of a John Cusack movie to this day.

This, despite all evidence to the contrary. Or at least the evidence of his latest film, The Frozen Ground, a real-life story from 1983 in which Cusack plays Robert Hansen, respectable family man by day and deranged serial killer by night. His serial killing USP being abducting teen prostitutes and then hunting them like deer through the Alaskan wilderness. Right up until cop Nicolas Cage turns the tables on him.

Cusack is, in fairness, convincingly serial killeresque. It's just a hard pill to swallow for those who remember that sweet boy from Stand By Me. But then a quick scan of his IMDb page and its ream upon ream of entries confirms what I've begun to suspect: he just seems to like working. There are eight movies and one TV drama listed for this year alone, and though some of them may have been filmed in other years, or may indeed be a figment of IMDb's slightly overactive imagination, he has, it's true to say, made a lot of movies. "Somewhere, like, 65," he says.

In fact, he's so impossible to pin down that after all requests of being on the same continent as him at the same time fail, I end up talking to him on Skype. I assume he's in a hotel suite somewhere from the view I have of the room he's in: there's an ugly office chair and in the background a shiny sofa and a coffee table on which is resting an ornate shisha pipe. It could be the Abu Dhabi InterContinental. But no – "It's a room off my kitchen," he says and takes a puff on what looks like Harry Potter's wand but turns out to be an electronic cigarette.

It seems like it was the fact that Hansen was such a "hard character to play" that drew him to the role. He read a book about sociopaths who have no feelings of empathy for other human beings. "And I thought: how would you portray that? I came to the terrible conclusion, after going around in circles, that he was having a good time."

Well, at least someone did. One early preview of the film notes that in the trailer Nicolas Cage "grimly intones the question: 'Have you ever seen anybody do anything like this before?'" The preview concludes: "Unfortunately, the answer is yes. A bunch of times."

It's fair to say that Cusack is a better actor than the role he's playing, but then his film choices in the past few years have been more than a little inscrutable. His recent films have either cast him against type – as in The Frozen Ground, or The Raven, in which he played Edgar Allan Poe, or 2012, where he battled against sci-fi disaster, or The Paperboy, in which he played another killer (though at least in this one he gets to play telepathic sex games with Nicole Kidman) – or have just slipped below the radar: The Ice Harvest, War Inc, Martian Child.

Is the serial-killer phase over, I ask hopefully. "Well, I didn't really choose it," he says. "It sort of chooses you. That's the way it goes." Though he describes it as "a journey where you're sort of going to the other side and seeing if you can come back without going crazy or becoming a drug addict or a psychopath".

It's not hard to believe. I feel cold just watching the film. It's set in the sub-zero Alaskan winter (which he filmed hot on the heels of The Raven in a sub-zero Serbian winter), and it doesn't look like it was the hugest amount of fun.

But then I have a feeling that fun is not the point with Cusack. He doesn't hang out at showbiz parties in LA. His main home, the Abu Dhabi InterContinental, is in Chicago, where he grew up and where his sister Joan also still lives, with her family. And even the briefest survey of his Twitter feed is enough to reveal that he's from the George Clooney school of relationship management. He's dated a string of fairly high-profile actresses (Minnie Driver, Hilary Duff, Lili Taylor), but has never been married and never talks about his love life.

And, also like Clooney, he's a committed actor-activist of the rails-against-the-neocons-on-Huffington-Post variety. He's friends with Naomi Klein, posts endless fanboy pictures of himself with Arundhati Roy on Twitter, and with rather acute timing helped launch the Freedom of the Press Foundation just a few months ago. Its mission is to ensure "transparency journalism" and to support whistleblowers, and it was co-founded by Daniel Ellsberg, the whistleblower behind the Pentagon Papers, and the board includes Glenn Greenwald, the Guardian journalist who first reported the NSA leaks.

This leak must seem like incredible vindication for what you're trying to do, I say.

But Cusack says it's just in his blood. His maths teacher mother and advertising exec father were activists – "And I grew up with the Berrigan brothers", an activist priest and poet who were at one time on the FBI's 10 Most Wanted list and who came from the same Mid-western Irish Catholic liberal intellectual milieu that his family inhabited.

"I was raised in a sort of salon-like atmosphere," he says. "Though I didn't realise at the time. I was just a kid, but as I got older I learned to appreciate it and to just try and pass on some of the information."

This latest leak, the Ed Snowden story, would make a terrific film. But he says what he most enjoys about getting involved in political causes is that it doesn't involve "trying to convince a bunch of bankers" to give him money.

Really, I ask. You can't see yourself playing Glenn?

"Glenn?" he says and looks surprised. "Oh. Right. I suppose I'm too old for Snowden." He is. Though I'm not surprised, he sometimes forgets this. He's been famous since he was 18, and the youthful Cusack of the Brat Pack years still burns brightly in the memory, though he says he can't bring himself to ever re-watch them.

"I had all my yearbook high-school photographs on film. All the embarrassing photos you look at and think: 'Oh my God, what an idiot I am' – I had entire films made of them."

The great advantage of early success, he says, is that he got his midlife crisis out of the way early. "I had it at 24, and it's nice to get it out of the way, because I've seen what happens when people get older and then they get famous for the first time and it kind of damages them. Whereas I was hot and then later in the month I was the next best thing and then I was cold. And then I got hot again – and you realise you can't take any of it seriously. You have to just find your way and try to have an authentic voice, and so it was very helpful in a weird way to have it all happen to me very young and survive."

'All the embarrassing photos you look at and think: "What an idiot" – I had entire films made of them': John Cusack in Serendipity (2001). Photograph: Allstar

And having been in the game for such a long time, he's the consummate professional. His PR cancels the interview at the last minute because he's been travelling all day, but then I get a message, and it's back on, and there he is, good-naturedly struggling to get his computer cam up and working, and puffing away on an electronic cigarette and prepared to answer questions that he gives no hint he's had to answer hundreds of times before.

He graciously simply ignores it when I fluff a question, and even though he finished filming The Frozen Ground in 2011 and I suspect that he's aware that it's probably not the greatest movie of his career – he says he hasn't seen it yet so can't comment on it – he still subtly manoeuvres the conversation back around to it, a loyal old pro to the last.

But then he's spent his entire career working with friends and family. He and Joan have appeared in no fewer than 10 films together, a number of which have also featured other members of the Cusack tribe – the other three Cusack siblings and his father Richard. He set up New Crime Productions with his old schoolfriend, the writer Steve Pink, and has frequently worked with another schoolfriend, the comic actor Jeremy Piven.

And some of his best work has been that which he has co-written and produced himself with New Crime Productions: Grosse Pointe Blank and High Fidelity, to name but two.

"You can do it," he says. "But then you have to think: 'Do I want to go through a war for a year trying to get something out?' And you think: 'Well how much time do you have?' And: 'Do you want to go enjoy your life a bit more?'"

But it's hard to avoid the feeling that John Cusack's best roles, his most memorable ones, are his most John Cusacky ones. He was a "little bit of Lloyd Dobler", the star of Say Anything, he's said in the past, and his real-life persona, talky, humble, isn't a million miles off the one he played in High Fidelity. You just seem to be a better ordinary Joe, I say, than you do a serial killer, or sci-fi star, or Edgar Allan Poe.

He doesn't disagree, as such; he just puffs away on his electronic cigarette and says that, by his estimate, he's made "15, maybe 20" good films. And "there are 35 movies that suck, so there you go".

"I couldn't make High Fidelity today," he says. Raising money to make your own movies is "just so hard". Though there's still some things he'd like to try. He'd like to adapt the classic Bulgarkov novel The Master and Margarita (would you play the cat, I ask him –"No, Professor Woland", aka the Devil).

I wish he would. In my opinion High Fidelity is that rare beast – an adaptation which was actually better than the book. He obviously has a talent for writing that I can't help thinking could be better channelled elsewhere than celebrity angsting on the Huff Post.

"Maybe," he says. And then with a puff on his wand, Professor Woland-like, he's gone, leaving nothing more than a blank screen and a question mark.

The Frozen Ground is out on 19 July