Agreed that much of the support for violence is due to the violence and oppression that they themselves (or else`their family and friends or else other members of their society) have suffered.
I think we have to look at the big picture: we allow ourselves to be divided and conquered. And it's not by accident - there are forces that deliberately and methodically pit us against each other in order to conquer us and pillage the world's resources and the products of our labor.
While I think Bill Maher does have a point (though it gets lost due to his hyperbole and careless way of communicating it), I think that most importantly he's missing the big picture. He's coming into the theater in the middle of the movie and, not knowing the plot, is misunderstanding the forces driving it. The real thing driving this catastrophe movie that we live in is the way the characters are manipulated, by offscreen actors, into fighting each other.
So while I agree with Maher's general thrust that religion has a part in this, I think he's missing that religion is not the ultimate source of the trouble, it's more of a lever that's employed by those who are the source.
The question then is how do we take the levers away from those who would use them to manipulate us. I think the answer is: good will. People of good will must seek each other out, recognize that the need is to work together on things that will save us all, and refuse to be manipulated into defeating each other, and thereby ourselves, over superficial differences. In other words, recognize that Othering is the main lever that we're tricked into using against each other and stop allowing ourselves to be used that way.
As mostly an aside, I think it might be the case that people of good will coming together would also deflate some of the drivers of religion and that religions might as a result diminish. Because religion is itself to some extent driven by Othering. And that diminishing would in my opinion be a good thing because it would be another way of taking some of the levers away. But it's not the primary way and therefore not the most important thing, because religion isn't the ultimate source of the problem, and that's what I think Maher is missing.