Why must different people of religions argue?

We don't have to. I have loads of friends of loads of different religions and we'd have "heated debates" but we're still mates in the end. I think the problem is that here no-one knows us so we're a little more outright about our thoughts, and maybe come across as rude. But in the end we're all human, so the rudeness and name calling is totally uncalled for. Atheists and Christians disagree belief wise, but being rude and calling each other idiots and monkeys is making us all look bad.