How do you deal with religious people?

I am an agnostic also european, I am in US and I meet people talking about god on every drop of the hat, you can see that they are brain washed, what bothers me the most is the '' god wants you to do this and not do that'' so far I've managed to avoid any confrontation and just keep things to myself but I find it hard not to hate these people for their imbecile believes. what do you say to a guy that gives you the argument '' because god wants us to ..whatever''