It should be acknowledged right away that some of the questions Jeremy Corbyn has been raising about the British and wider western response to the latest Islamic State-inspired atrocities in Paris are legitimate ones.

The problem is that the Labour leader is not the man to ask them, he doesn’t have enough credit in the foreign policy bank. After a lifetime of rebellion against his party, he’s in no place to lay down the law on that looming vote on whether to extend airstrikes to Syria either.

No wonder some Labour MPs got cross at Monday night’s weekly meeting of the parliamentary Labour party (PLP), over both the leader’s evasive-to-the-point-of-dishonest remarks on TV in recent days and some made in the room. Politics is either about posturing or about the pursuit of power and the focused discipline that entails. At a time of crisis it is not about one’s “zany” love of drains, of which more later.

The point is easily illustrated by contrasting Corbyn’s position with that of David Davis, the recidivist backbench Conservative rebel on civil liberties, Edward Snowden and much else in the conventional wisdom department. He’s a natural troublemaker, it suits him. But he is also a hard man and everyone knows it, as Corbyn is not.

A Thatcherite former Europe minister, Davis gave up a lot to rebel, including the near-certain prospect of cabinet office when he resigned to stage a quixotic “civil liberties” byelection in his own East Yorkshire constituency in 2008. I thought he was wrong. David Cameron’s cabinet of folk with soft hands would be much improved by the presence of a street-smart working-class boy, born to a single mother and raised on a south London council estate. But you had to admire his self-belief.

None of the above paragraph applies to Jeremy. Even that name (his eco-brother is a Piers) is a giveaway. Raised in middle-class comfort in Shropshire to well-meaning progressive parents who met supporting the Spanish republic (poor health prevented dad from fighting) their fourth and youngest son slipped easily into the world of public sector politics and, at 34, became the leftwing MP he remains now. His worldview hasn’t changed, though the world has.

Many Labour activists and inactivists, the ones who elected Corbyn as their leader by a landslide in September, will protest that this is unfair. Many fair-minded Guardian readers who support other parties of the centre-left and left will agree with them. They chide me on Twitter when I show impatience with the evolving Corbyn project.

A little bit of me agrees with them too: it’s important to be fair. And, as I keep on telling people who ask: “Jeremy Corbyn is a very nice man, nice but naive. Some of those around him are neither.”

Where I agree with the Corbynistas is that a leader elected by such a resounding majority cannot be overthrown by a parliamentary coup, any more than I think the half-baked plotters in the Corbyn camp dream of deselecting Labour’s “traitor” MPs and replacing them with good comrades.

So if Corbyn goes before the 2020 election it will because he will be almost 71 on polling day and feeling very battered and beaten by events. The rest is fantasy talk unless Unite’s Len McCluskey decides “enough is enough”. He hasn’t got the balls.

If they are sensible, both sides will fight for every inch of control of the party machine, but reach an uneasy accommodation in public. It will be left to voters to pass judgment on the result, starting at the May local elections in 2016.

Decent people, some my own age, friends of many decades living in expensive suburbs, get cross when I say: “I know the outcome, I’ve seen this movie before.” They reply: “Look at Syriza, Mike, look at Bernie Sanders in the US. This time it’s different.”

There’s no point, so I find, in me saying, “Indeed, just look at Syriza, split and in full retreat after 10 months of office in Greece.” Or, “‘This time it’s different’ are the four most dangerous words in politics. It rarely is different.” I meekly say: “You may be right. Humility all round is what’s called for.”

This week’s crisis over Isis could instead have been about economic policy, as George Osborne still hopes it will be when he delivers his autumn statement. In fact, the chancellor’s cockiness may be Corbyn’s best bet. On Tuesday, Osborne’s visiting GCHQ, but he’s the last man who should be speaking in Cheltenham about extra funds for cybersecurity. He may be right, but it’s Theresa May’s job, not his. Voters will rightly suspect he’s playing politics at the expense of a rival. He often does.

So Osborne is like Corbyn in one sense: the wrong man saying the wrong things at the right time: a serious threat to the security of western states. The difference favours Corbyn as a human being. Over the stepped-up bombing of Syria, the questionable legality or morality of drone strikes like the one which killed Mohammed Emwazi (even military hawks like Max Hastings have qualms), the trigger-happy instincts of armchair strategists, he is saying what he has always said. Ditto the Trident nuclear debate.

That’s Jeremy, say his admirers, he’s honest and he’s consistent and (add some) he’s been right in the past, as those beastly Blairites were WRONG, WRONG, WRONG. Nothing I can say here will change those sincerely-held opinions, callow though many are. If you think the IRA accepted Belfast’s Good Friday agreement out of goodness or a change of heart – not military exhaustion and penetration by the security services – good luck to you. If you think Isis arose from the US invasion of Iraq, not the vacuum created by its inept occupation and premature withdrawal, good luck again.

Unfortunately Jeremy and some of his allies do think all that. Jeremy sincerely believes that by talking to Sinn Féin/IRA, to Hezbollah and Hamas and their kind, he furthered peace. Perhaps he did, but the shitty work in any peace process is sitting down for endless hours in grubby hotel rooms with people you loathe as well as with your “friends”. The world can be a rough place where everyone except Angela Merkel can do bad things for bad reasons, even Vladimir Putin.

On a ITV sofa show this week Corbyn was lured into discussing what he calls his “zany” interest in drains. It’s a hobby which does no harm, he explains. Charming and true, but not right this week.

Which brings us to the Stop the War Coalition ( STWC) – here’s a potted history – whose “Paris reaps the whirlwind of western support for extremist violence” tweet caused such offence to MPs at the PLP. Corbyn called it “inappropriate” and insisted on its withdrawal, but he wouldn’t condemn it.

How could he? He’s been a STWC activist from the start and was – perhaps still is – to be a star speaker at its Christmas bash. Check out its website here. You may agree with most of what it’s saying, I’m sure I agree with bits of it, but mostly not. The perspective provided on world affairs by a familiar coalition of Trots, communists, peaceniks of the inter-war kind (check out the Peace Pledge Union) are a mixture of the well-meaning and brutally geopolitical or utopian. None of them can spell “China”. And Isis won’t distinguish them from us when and if the great day of the apocalypse comes. Try this scary, long perspective on the Raqqa comrades who seem bent on taking on Europe, the US and Russia, whose plane Moscow now concedes they blew up. Whatever they’re on, it’s strong stuff.

None of which means that Corbyn’s analysis is all wrong or the other side right. By all accounts the hugely experienced Hillary Clinton was hopeless and evasive in the Democratic hopefuls latest TV debate: as the public mood hardens, she’ll pay a price too. President Marco Rubio, anyone?

So when Corbyn says “Jihadi John” should have been brought to trial for his dreadful crimes instead of evaporated by a drone, he’s not providing a real alternative except to let him go on head chopping and making YouTube videos. As Labour’s shadow foreign secretary, Hilary Benn (struggling on Radio 4’s Today show to keep the team united) says “there is no realistic prospect of him being apprehended” so rough justice was the right, rough choice.

Time and time again Corbyn ducks saying things like that, preferring to shelter behind platitudes like “give peace a chance”. As Barbara Castle once chided her old pal, Michael Foot, he’s “grown soft on a diet of soft options,” not quite a pacifist (so he says) but opposed to passing wars and the legitimacy of force in a harsh world.

For an honest man, that’s not honest and the voters will notice sooner or later. Possibly sooner.