Why is politics so nasty and crappy at the moment? Why does it feel so rootless and shallow? Why did Canberra this week feel like a grudge match between the Visigoths and the Zombies? What the hell is going on with the people we elected to the 150 seats of the House of Representatives a year-and-a-bit ago?

Do you feel like you've been asking this question for a while now? Me too. I've been covering politics since 1999 and I've never, until this year, ever sat in the press gallery, looked down and thought, "I actually don't think I can bear another second of this."

I think I've worked out what is so frustrating. It's not that the parties can't find agreement on anything. It's that they're not even looking.

Let's have a look at the two main issues on the slab this week in Canberra - climate change legislation and the proposed changes to the Migration Act.

These are two absolutely classic examples of the problem assailing Australian politics right now. Both of these debates have achieved what I call full meta-political liftoff, which is to say they no longer actually concern, to any real extent, the actual policies they purport to involve.

Debate on the carbon tax is no longer anything to do with whether climate change is real, and what we should do about it. The debate is about whether Julia Gillard is a filthy liar, and whether Tony Abbott is just a grubby opportunistic hypocrite.

The immigration issue, meanwhile, is no longer really about the matter at hand - the nightmarish moral balancing act between maintaining authoritative Australian borders, helping the most needy and discouraging the desperate from putting themselves and their children in danger. It's about whether Julia Gillard is a hopeless incompetent, and whether Tony Abbott should rescue her.

Imagine the debate about asylum seekers as a policy spectrum.

"A" might be expanding the humanitarian intake to accept and assist all unauthorised arrivals, and allowing them to live in the community while they are being processed. Then maybe helping them to get established, and to bring family members to Australia too.

"Z" would be withdrawing from the UN refugee convention, and sinking a few billion into heavily armed gunships to patrol Australian maritime perimeters 24 hours a day, repelling unauthorised craft and refusing to rescue people in the water.

From the heat and vituperation involved in the exchange this week, you'd be forgiven for thinking that the major parties occupy positions at about "D" versus "W". Actually, I'd say they're both at about "Q", give or take a few consonants.

And that is the grim secret of this particular policy issue. They actually don't disagree that much. Both parties want to do as much as they can to wiggle out of Australia's formal commitment through the refugee convention, which is to protect people who come here if they have a valid case for protection. They wiggle out of it by redrawing Australia's boundaries – they've both done that. They wiggle out of it by trying to exclude asylum seekers from the Australian legal system – they've both done that. They wiggle out of it by trying to avoid having asylum seekers set foot on Australian soil, and by processing them in other countries. They've both done that.

And yet they're at daggers drawn, for reasons that are all about beady-eyed political manoeuvring. The Government's desperate to get a solution that will rescue it from public suspicions that it is irretrievably incompetent in this area. It must keep alive the perception that it differs from the Coalition on border protection, because to concede otherwise would be to admit the emptiness of its 10-year internal death-struggle with this issue.

The Coalition, meanwhile, is tossing up the matter of perceptions, in a debate with itself that goes like this: "Hmmm. We could support the amendments, which would make us look gracious and constructive (good), but would also let that hopeless, illegitimate, witch of a PM look good (bad). Or we could reject them, which could mean that we might get blamed for boats arriving (bad) but could very well mean that the Government would be blamed for it (good)."

When the Prime Minister made her offer of bipartisanship on Monday, it was with all the charm of a fishwife presenting a past-its-best flathead to a hostile customer at five past five.

"I'm making this offer to Tony Abbott, even though he's a dumb, opportunistic wrecker who is savagely indifferent to the national interest," was in effect her sales pitch.

And Mr Abbott returned the compliment in Parliament, replying that it was not his job to pick up after her disasters, especially when she was such a crotchety old hag about the whole thing. And so on. For a couple of people who more or less agree on this stuff, they sure hate each other a lot.

And this is the tragedy of Australian politics – not just this year, but for a long time now. The great weakness of our political system is not the hung parliament, (although that does tend to make everybody act like they're on ice the whole time, which is certainly tiring).

The great weakness of the Australian political system is that it is incapable of reaching agreement, even where agreement essentially exists. It wears itself out on fights that aren't really fights. We might think of our great old political parties as prize-fighters, but they never even get to the ring; they're too busy punching each other to death over who gets the dressing room with the comfy couch. No wonder the crowd's restive.

On climate change, this nation essentially had consensus in 2007; our politicians applied themselves diligently to the situation and four short years later we've got a pile of political roadkill, a confused and hostile electorate and two protagonists who nobody likes, shouting themselves hoarse while their offsiders go through each others' bins.

On immigration, two parties who essentially agree with each other are determined to find and exaggerate their differences, because to acknowledge their agreement would be either a tactical blunder or a confession of utter political nihilism.

Never have the 1980s, a decade in which governments and oppositions did unpopular things together in the national interest, seemed so distant and foreign. And that's because the concept of agreement has changed somehow, from being something noble to being something weak. It's a scary development. I completely agree, by the way, that the media plays a role in this. We fetishise conflict over consensus in a way that certainly encourages the invention of differences, even where none exists. I accept that. But it can't be the whole reason - can it? Is it because after the end of the Cold War, the field of real structural and philosophical issues over which domestic politicians can fight is contracting? And if that's the case, then why do we spend the money on having a parliament?

Or maybe it's just been a bad week. What do you think?

Annabel Crabb is the ABC's chief online political writer.