Deadliest religion ever?

[Crunchy]

I also think that statement by Stephen Weinberg is false too, I think that other ideologies can influence people's behaviour just as badly as religion.

I sort of agree with you on this but I believe that religious ideologies can be especially bad (see below in my comment) However that leads to the question of what it takes to get good people to do bad things. 

IMO, it involves faith.
Not faith in other people mind you, but faith in ideas, even when espoused by someone you trust. I think that we must have some faith in those around us even if it is sometimes misplaced. But faith in beliefs and ideologies... even secular ideologies( but especially religious ideologies) is pure evil. 

The only difference between religious and secular ideologies is this:

Secular ideology: I think we should live by rules X, Y and Z
Religious ideology: God told me we should live by rules X, Y, and Z

The reason that secular ideologies are better is because when asked to defend your secular ideology, you have no choice but to make some attempt at a rational argument. With a religious ideology, all you have to say is "because god says so", no more thought required. One invites rational thought (even if people often fail at rationality) and the other rejects it out of hand. I think this is why religious ideologies can sometimes persist for thousands of years whereas bad secular ideologies seem to burn out.

Perhaps this is why Weinberg singled out religion.