So let me put it in simple and straightforward language:
I do not particularly care what motivates people - be it imaginary heavenly creatures or anger over the course of events or policies that I strongly oppose as well. All I care about is people's deeds. So if someobody decides to blow up innocent people selected at random - I care very little whether his motives are justified or not - all I care that this guy be stopped in the most effective way possible. Blowing his brains our before he blows other seem to be such a way, and I think that the British police (who btw are not known to be otherwise trigger-happy) are using the right strategy given the situation.
I furthermore think it is utterly foolish to fail to obey orders of the police in a situation that is likely to provoke their overreaction. Again, I do not know what Mr. De Menezes was thinking but he made a very grave mistake indeed when he decided to run. His death was a tragic mistake, but frankly I do not think that most people would appreciate if the situation turned some other way i.e. the suspect getting away or carrying out its mission because the police hesitated to use the deadly force to stop him.
Wojtek