If you want to see how far a certain kind of contemporary liberal will go in order not to have to recognize something perfectly obvious about one brand of modern terrorism, you need look no further than a piece by Oliver Burkeman going under the title 'What caused the Boston Marathon bombings? It's complicated...' Oliver begins from commentators - apparently including Andrew Sullivan - who think that those who carried out the Boston bombings were motivated by their religious views and that this is 'a sufficient explanation'. Oliver isn't satisfied, and rightly not. However complicated the issue might be, one thing that is very simple to observe is that the vast majority of religious people and, more specifically, the vast majority of Muslims do not go around murdering others by the random placing of bombs. So the religious views of the perpetrators is not a sufficient explanation for acts of terrorism.
Oliver goes on to say the matter is complex, as it surely is, that 'what constitutes an "explanation" is irredeemably murky', and that deploying the concept of 'evil' won't resolve the difficulty. He contrives, however, to pass over the observation, just as simple as the one recorded in the paragraph above, that there has been a strong correlation in recent times between people committing acts of terrorism and adherence to a murderous ideology - called sometimes Islamism, sometimes jihadism. This does not mean that that ideology is, for its part, a sufficient explanation of acts of terror. But it is a reasonable hypothesis that the ideology is a large contributory cause of terrorism. In social explanation it is entirely common for no single cause to be sufficient in itself, but that doesn't show that no putative cause is ever of significant weight. People adhering to an ideology justifying random mass murder of civilians are more likely to murder the innocent than, say, sincere pacifists, Quakers, a cross section of cycling enthusiasts, members of the Labour Party, and so on. In just the same way, young men rejoicing in racist attitudes towards immigrants are more likely to commit acts of violence against them than are those of cosmopolitan outlook - or sincere pacifists, Quakers, a cross section of cycling enthusiasts, members of the Labour Party, etc. This bit isn't all that complicated therefore.
Just to be clear here, Islamism/jihadism is not unique in justifying the terrorist killing of innocents. The IRA went in for the same kind of thing on the basis of ideas having nothing to do with Islam or Islamism.
In his yearning for complication, Oliver decides to throw in the following at the end: 'sorry to bring this up, but free will might not exist'. Well, if it doesn't then the 'benefits' of its non-existence in acquitting people of responsibility for what they do will need to be extended to racists, torturers and those who wage wars that Guardian liberals typically oppose - to categories of people, in other words, they tend not to wring their hands about. Oliver describes himself as 'the worst kind of handwringing liberal'. Fortunately, there's another kind of liberal - one who can see what is both simple and clear in the connection between ideologies of hate, on the one hand, and terrorism, on the other, and who does not run with the oh-so-complicated obfuscation.