It's a little alarming to think that, in the space of a matter of weeks, two seasoned Labour politicians have stood accused of racism.

Backbencher Paul Flynn MP had always seemed like a fairly sensible lefty, until he one day decided to question the suitability of our ambassador to Israel on the grounds of his Jewishness [2]. And, on Wednesday night, Diane Abbott came close to losing her Shadow ministerial post over a tweet [3] which read "White people love playing divide and rule. We should not play their game". A comment which, as many observed, would surely have been a career-ending move for any politician had the word "black" been switched for "white" .

However, in the resulting Twitter-storms over both, we saw some examples of the opposite: the extraordinary logical contortions that people can be prepared to go through to defend an unacceptable view. It was notable, though, that these defenders, on issues which are not essentially-party political, seemed to come exclusively from the left of the Labour Party and the liberal-left media. In contrast, in the country at large, the condemnation, especially of Abbott, was widespread.

We need not go over again why her comment was unacceptable. But most worrying of all was the mindset that it gave us a window into: a thinking which separates "us" (black people) and "them" (white people). Most modern Britons, it may surprise Abbott to know, don't think like that. Now, Labour has obviously learned from Flynn, and this time things were handled considerably better: the apology was swift and Ed Miliband called Abbott immediately, in the middle of a Sky news interview [4], to give her a dressing-down.

With Flynn, part of the negative story was the shockingly long time - a whole week - that it took to get an apology, and the fact that the leadership seemed rather hands-off (the disciplining was left to the Chief Whip [5]).

We might reasonably conclude that this better handling comes as a result of the outcry from the Jewish community about Flynn; the relative seniority of Abbott; and the fact that Miliband, in this latest case, does not have to deal with the issue of sensitivity to his own Jewish origins.

And yet, we are left unsatisfied: Diane Abbott is still in post when a Shadow minister making generalisations about "black people" clearly would not be. And it is also arguable that even then, had she been in another political party, her colleagues might not have been so understanding. For example, the Tories take any hint of association with racism or fascism very seriously nowadays. Aidan "Nazi stag party" Burley was only at the most junior level of government, but Cameron made a point, not only of sacking him, but commissioning a further investigation. Neither had Burley, despite his offensive behaviour, made any comment which anyone deemed racist.

Yes, there is a common thread which joins Flynn and Abbott: both exemplify the casual tendency on the left of the Labour Party to tolerate the intolerable when it comes to race. And not just what is said: who says it is important. In this case, it seems that we are obliged to treat Diane Abbott differently, as a talented young blogger, Stephen K Bush, has pointed out [6]; as if black people were somehow incapable of racism.

I don't know how many times I have been stopped and searched. But I do know that it is an experience that not one of my university friends has ever undergone and is ever likely to undergo, because they are white, and I am not. But fortunately, it turns out that this means I can say whatever the hell I like about white people apparently, without any fear of reprisal, because I 'can't' be racist, at least according to the vast edifice of Diane Abbott apologia that has been erected on the Internet today.

And, it is worth noting that whilst, in the left-Labour blogosphere, you can indeed find many who defended Abbott, you can also find many like Stephen who feel mounting frustration with that kind of apologia in the party we love.

I believe Diane Abbott is not a racist. And neither is Paul Flynn. But both expressed totally unacceptable views. And it was not as though something slipped out which was misinterpreted in either case; that is a shabby twisting of the facts. MPs live and die - rightly - by the words they speak, and in neither case was there a reasonable alternative reading of those words.

The conclusion to all this is a simple one: that the Abbott affair is not about colonialism, as she risibly claimed; just as the Flynn affair was not about the Palestinian question. They are about the tolerance of the left to attitudes on race that the centre and the centre-right would have no truck with. An extraordinary reversal, from the party that once fought apartheid, and a tragedy.

Rob Marchant is a political commentator and former Labour Party manager who blogs at The Centre Left [7].