True, it's not the only factor at all, but it does play into it. It's just like with marijuana prohibition, conservative (some say radical) religious views cloud the ability to see fact and reason. Yes, European nations are also predominately Christian, but not in the sense that the US is. There is not a movement of Southern Baptist, Methodist and even more far leaning sects that there is here, and those far right leaning religious groups aren't as readily elected into office as has been known to happen here. Comparing the US to say, France on the basis of Christianity is similar to comparing Kuwait or Turkey to say, Afghanistan on the basis of Islam. Same religion, yes, but very different ways of incorporating that religion into daily life and law making.
It's not all about religious belief, not even close, but this nation's collective misunderstanding of the "state" religion does play heavily into some of our laws.