First of all, you're never going to be able to understand and co-exist with religious people if you're so offensive and insulting toward them. Show some respect and you'll get it back.

Secondly, if you talk to your parents about religion the way you did in this thread, then it'll only confirm their assumption that you need religion in your life - they'll think you're going 'astray' or that having God in your life will help you.

Be calm, be respectful, try actually learning something about their religion, and try and learn why they want to have religion in their life. Then you can explain to them (calmly is always the best way) why you don't feel that you need religion in yours. Hopefully both sides of the discussion will come away feeling like they have learnt something about the other, and it may strengthen your relationship. By talking to them about what they believe in like you talked about it in this thread, both parties will only come away feel angry, misunderstood and offended.

Good luck.