Well if you make claims about the world based on a little book written thousands of years ago you open your views up to ridicule. If you are insulted because you don't like your views being scrutinised then that is unfortunate but hard to avoid. I think you can debate this without insulting the person directly while criticising their wishy washy set of unsupported ideas though and I don't think there is anything morally wrong with that, quite the opposite
I think a lot of atheists get some kind of self gratification from trying to make other people look stupid though, which doesn't necessary help people to understand why they are wrong. They can just end up having an "us vs them" idea in their mind where it becomes personal and missing the real point of the debate
"...why they are wrong"? Nobody is right, you know. Why not let people believe what they like, aslong as its not dangerous? If it keeps them away from lets say, stealing my car or murdering me, be my quest. I went to couple of religious lectures back in my day and it kinda opened by eyes. Not to Jesus, but...other things. There were people there that stated they had almost drank or OD-d themselves to death, until they found socalled "peace". No psychiatrists or anything other managed to do that for them. And they seemed like really nice people. They were religious, but they kept their mumbojumbo to themselves, if I said im not, so we talked about other stuff. So practically it did save them. They would probably be dead or in jail by now. Religion has its good and bad sides, just like everything else. So why not let a person believe whatever? Assholeism does not have a special religion, country or skincolor. Whoever states that its all bad has clearly only scratched the surface of the subject.