While it may be true that a load of atheists hate the fact that humans are allowed to believe retarded shit, I think a lot of it is down to the fact that much of that retarded stuff affects them, personally by way of stupid laws that govern what they can and can't do. I think this is becoming less of a problem on aggregate as rational secularism generally prevails but you don't have to look far to the fringes to see that there's still some seriously fucked up shit happening because god.
I think the above is true. Many atheists are just trying to save others from the percieved consequences of their beliefs. We behave stupidly either way, and then develop our reasons to taste with the cause that is convenient.