To say that a suicide bomber "dies for his beliefs" can be expressed in a single word: martyrdom. The problem is that this gives a certain legitimacy to the act. Martyrs can be revered for having the courage of their convictions in the face of certain, possibly painful, death -- except that historically martyrs had a tendency to die for their beliefs without also killing a dozen or so bystanders at the same time. And that changes the nature of the act from a religious sacrifice into mass-murder.
It's also not all that he said -- Livingstone was not-so-subtly shifting the blame for 7/7 from the innocent martyr-esque terrorists who were compelled into this noble act of self-sacrifice by religious considerations in response to an invasion of their country, and giving it instead to that evil cruel *** leader who attacked Iraq in the first place.
I think a lot of people on AB feel that Tony Blair has a lot to answer for, and certainly the Iraq Invasion has turned out to have been less than successful (understatement) -- but is responsibility for 7/7 his, as Ken Livingstone stated (and not just implied, either, but directly stated)? Absolutely not. As in many other cases, people have a tendency to conflate poor decisions made by victims with responsibility for the crimes committed against them. But there is no justification, whatsoever, in any way, for blowing yourself up in a train, or on a bus, or marching into a concert hall, and killing people indiscriminately.
We need to be careful in the language used around this. Western policy in the Middle East has been a failure, but that does not at all mean that it is directly responsible for the response by some of turning to terrorism.