Sometimes it's down to the director-general of the British Retail Consortium to sum up the national mood. "Non-food is having a thoroughly miserable and difficult time," he said last week. He's so right – it really is. And, of all the non-foods, the humans are particularly depressed, with more than 2.64 million of us now out of work. But I like his note of optimism. We remain non-foods. We haven't started to eat one another. While we've not yet been reduced to carrion or prey, there are still grounds for hope.

We're in the grip of a historically significant slump, possibly as notable as the Great Depression. Our current trials will definitely be on the A-level history syllabuses of the decades to come. Any more disastrous developments and we may even make GCSE.

The question the kids of the future will be trying to answer is: "What caused all that suffering?" As a former lazy history student myself, I know that the trick here is to look for the point in the debate where someone says: "It's a bit more complicated than that" and then go back to the previous assertion. The things that historical events are a bit more complicated than are, in my experience, also the things that they basically are.

Proper controversy is when one historian says: "This is caused by Thing A" and another says: "Shut up, you! It was caused by Thing B." But when one is saying: "It was Thing A" and the other says: "It's more complicated than that", I reckon we pretty much have an answer. Some say it's Thing A, others say it's partly Thing A – that's as close to a consensus as naturally argumentative and contrarian people (which is a tautology, and you'll only prove me right if you disagree) are ever likely to come to.

In the case of our current troubles, the thing that it's a bit more complicated than, but it also basically is, is "all the bankers' fault". I know my saying that will annoy some people, but that's OK because they're the very people I take most pleasure in annoying. So if you're thinking about getting annoyed, you might want to consider not giving me the satisfaction and agree with me instead.

Last week, the Financial Services Authority finally offered its considered opinion that the collapse of RBS in 2008 was caused by "underlying deficiencies in RBS management, governance and culture, which made it prone to make poor decisions". It's easy to take the piss out of this because it's a bland statement of such a self-evident fact; but it's like when a mishit at Wimbledon flies off into the crowd – a linesman still has to call "Out!" when it finally hits the ground.

So it's clear that, while other factors must be borne in mind, such as feckless midwestern property developers, consumers spending beyond their means, Greek fiscal imprudence, George Osborne's point about the snow and George Osborne, we'd be in shallower shit now if more bankers had got theirs together. This is why I'm worried about Bob Diamond.

Barclays' new boss first came to my attention in January when he told MPs that the "period of remorse and apology for banks … needs to be over". I didn't like that, partly because I hadn't really noticed any period of remorse and apology, unless you count "I'm sorry our various scams didn't work" as an apology; and partly because it's not for him to say. If you're really sorry for something, you should just keep being sorry. It's for others to decide when you can be let off the hook. If you're the first to be asking whether you've apologised enough, then you haven't.

Now he's changing tack in a way that makes his judgment seem even more questionable. In an interview last weekend, he said he'd introduced a "no-jerk rule" that had led to his parting company with more than 30 senior executives. "If someone can't behave with their colleagues and can't be part of the culture, it doesn't matter how good they are at what they do, they have to be asked to leave," he said.

This doesn't make sense. Since well before the crisis began, investment bankers, and indeed all top City executives, have defended their stratospheric pay deals on the basis that, in the cold light of economic reality, they were worth it. They got the big bucks because they brought in the bigger bucks. They possessed rare profit-making skills. They had the magic touch, everyone was crying out to employ them, so being paid millions was nothing more sinister than the market functioning as it should.

But what Bob Diamond appears to be saying is that he's willing to sack the goose that lays the golden eggs for being rude to its PA. That can only mean one of two things: either Bob is an incredibly poor, albeit principled, businessman and, regrettably, Barclays probably needs to look for someone harder-nosed; or highly paid bankers aren't geese that lay golden eggs but are eminently replaceable. If so, why are they so highly paid? Is being a jerk specifically harmful to business acumen? I'm afraid I don't believe it is, even if I'm willing to accept it isn't necessarily helpful either (which I only am when I'm in a very good mood).

Diamond cites the example of six Barclays bankers who spent £44,000 on wine at a posh restaurant in 2001 saying: "to have acted that way in a public place is inexcusable". I don't understand this either. It was their money. If you want to make sure your employees don't spend tens of thousands on wine, don't pay them millions. Otherwise they'll spend it as they like, whatever the PR cost to the company. To do otherwise would imply that they were ashamed, that the money was ill-gotten, that they were bank robbers not its employees, and being careful not to attract suspicion.

Wayne Rooney doesn't seem like a model employee. I'm not sure he'd survive a "no-jerk rule". Conspicuous consumption is the least of his PR crimes. Yet he evades the sack because his talent is undeniably rare. What Diamond's remarks reveal is that the same cannot be said of bankers who enjoy equivalent remuneration.

If Diamond isn't bright enough to grasp that what he said, far from being canny or diplomatic, fundamentally undermines his profession's justification for existing in its current form, then it's clear that we're still in the era of overpaid mediocrities running banks.