I don't think so and think there are far more wrongs on the loyalist (british government even if you like) side. I agree that injustices can bring out the worst in people and situations can create terrorism - I feel that way over our governments stances over Iraq, etc. But there in lies a question:
Let's say the muslim case is strong... at what point would you justify the bombing of innocent people in London to uphold the cause? The IRA in my mind have done that and even if you chose to paint people who will do that whiter than white, I'm afraid I don't.