Look, everyone seems to be missing a fairly important point here: faith and religion, though often connected, are not the same.
“Faith in god(s)” isn’t by itself a bad thing.
The problem is that people who choose to have faith in a deity (and yes, it’s a choice) generally choose to have faith in certain other people too, and faith in texts that purport to be the word of god(s).
In other words, having chosen to believe in whatever supreme being you’ve picked, they realize that they have no idea what god X actually wants of them. So, they go to a church, synagogue, mosque, mandir, or whatever, and find someone else to explain it to them.
That’s when Bad Things happen, because the person you’ve put your faith in is either a) making it up as he goes along, or b) regurgitating what others have told him.
Maybe he just says “love thy neighbor”, which is okay. More likely, he also says, “and by the way, don’t do X”, with the usually corollary being that people who do do X are Bad.
Once you start judging actions that aren’t instinctively recognisable as wrong (murder, theft, rape, etc.), the possibility of doing evil in the name of your faith appears.
But what about, say, abortion clinic bombers who don’t go to church or wherever? They’re still influenced by others. They may not actively seek out others to interpret their faith for them, but they’re still hearing other interpretations and internalizing them (or some aspect of them).
The biggest problem with all this is that most people don’t put any thought into their religion or faith. They believe what they believe because that’s what their parents believed, and they listed to whoever they listen to (pastor, vicar, priest, other cleric, Rush Limbaugh) because that’s who the people around them listen to.