"Increasingly, there seems little doubt that Iraq was, at the least, one of the motivations. It _may_ well have been the tipping point for the persons in question."
And America's subservience to the Zionist Occupation Government was Timothy McVeigh's motivation for the Oklahoma bombing, western society's subservience to technology was the Unabomber's motivation, while the Son of Sam was told to kill people by his dog.
Iraq might have featured in the London bomber's motivations (which of course we cannot know because they declined to tell anyone why they were killing them) but who knows what stimuli could have triggered this psychotic response. The error here is to try to force an irrational act into a rational explanatory framework, as if to tame it and make it sensible.
And I don't agree that Islamic terrorism is on a par with anti-imperialist movements, like the 'physical force' Irish nationalists, or the PLO. They did kill people, which is raises the stakes, but they also held themselves accountable to a popular base. Even the Mau Mau in Kenya, under the most atrocious repression, sought to mobilise mass opposition to British rule, and thereby tested there campaign in the eyes of the Kikuyu.
The Al Qaeda inspired terrorism in Europe and the US, by contrast, uses violence in isolation from any popular struggle. Even though Iraq features (along with a lot of less intelligible stuff) in its sporadic communiques, there is little evidence that these individuals are hold themselves accountable to any human authority. A lot of the arguments - that the Arab states and most Muslims are not really Muslims - express the contempt these individuals feel for the judgement of their fellow men and women. Organisationally, clandestine organisation and small cells insulate these bombers from popular judgement. The tactic, suicide bombing, relieves the individual of facing up to the messy human experience of the atrocities they leave behind them.
In Algeria, the FIS did contest elections in the aftermath of the first Gulf War, when the remnants of the Nationalist government had lost support for supporting Desert Storm, and they won the majority of the country, which was a significant new departure for the Islamist. What's more the repression that followed ought to have seen the FIS consolidate that popular base. However, their own tactics were widely seen by Algerians as brutal as the authorities, and they haemmoraged support.
The frittering away of the FIS popular base in Algeria was one of the key event that consolidated the shift towards all-out war against the US - an attempt to galvanise support by military elan. That did have a spectacular effect, but it has singularly failed to create any enduring movement and for good reason: it was a strategy that was designed to by-pass the difficult task of winning over mass support by individual action.
It is not popular opposition to the war in Iraq, but the lack of popular support for the ideas of Al Qaeda that pushes its activists into terrorism.