It's the not even just the reason for the death toll, the deliberate cruelty of it. A big part is that it was all over the media in such detail that we had no choice but to really feel it.
Blair condemns it, despite being directly responsible for exactly the same thing. Explosives going off randomly in a city, killing whoever was unfortunate enough to be nearby, in an attempt to use the violence to force social and political change.
One person I said this to told me I was 'piggybacking my politics' on to it, using a tone which made it clear he thought I was well out of order.
The implication was that opposing and being revulsed by bombing Baghdad, Kabul, and a dozen other cities that never get a mention on the news is somehow just an intellectual point-scoring game, whereas the London bombings are something more real, above political concern.
This basically says that Iraqi, Congolese, or Afghan deaths aren't as real and worthy of grief and outrage as the London ones. We have a word for such ideas; racism.
I think it's just that my critic had never properly considered, really imagined, what it must be like to be in the marketplace when a B-52 lets its payload drop on it. If there's any good to come from the London bombs, let's hope some of it will be a heightened awareness of what bombing actually means.
Be it Baghdad or London, from a plane or on a train, all bombing is terrorism.
There have been a couple of public demonstrations of solidarity in London, as there was in Madrid, and numerous 'you don't scare us' pieces written, like this.
Despite appearances, they are not really addressing the terrorists. They are for the benefit of the writer and those in London who want to carry on. We cannot seriously think the terrorists' aim is to make everyone in London too scared to leave the house. They are, therefore, doing it for other reasons.
Other recent terrorist attacks have been from those wishing to sow a sense of insecurity among the citizens of the city concerned because of its occupation of holy lands, and to widen the rifts between the decadent and the devout, to stop Islam from fitting snugly in the west.
For all the 'we'll pull together' spirit, since 9/11 there can be no doubt that there is indeed greater mistrust of muslims. In the days after the London bombings there were random vandal attacks on British mosques.
This is compounded by the heightened racism in Britain. I seriously doubt whether Jean Charles de Menezes would have been followed and shot if he'd had blue eyes and blond hair.
Additionally, the popular idea that the bombers are evil - that because their means are unjustified they are therefore without reason - fuels the dehumanising, and the wider racism. In taking this stance we do our bit to increase the divide and, as Gyrus says, prevent ourselves from finding solutions.
Public discussion on the crucial issues here is crippled, as ever, by basic logical errors. We conflate the condoning of terrorism with understanding terrorism. As anyone will agree (in any other context), understanding a problem is pretty much a prerequisite to solving it; therefore, in this simple, scared way of thinking, our fear of capitulation to the forces of barbarism instantly scuppers any chance of moving past this dark phase of history.
It's not just the overt racism of the mosque vandals that needs to be opposed, but the more subtle racism that allows us to think fifty people killed in a Baghdad bomb is no big deal, and nothing to do with us.
The key element of the London solidarity vigils, yet it isn't really being pushed into the public arena hard enough, is that London is a wilfully multi-ethnic and multi-cultural place, and that's the way we want it.
For all the demonisation of the Republicans during the Irish Troubles, we always understood they had reasons, and there weren't random attacks on Catholic churches. This led to a cessation of violence.
This time, much of public opinion is pushing the other way. It's this lack of understanding and deepening of racism - rather than not catching a bus - that is letting the terrorists win.