Why does religion in way of Friendship or any other public affairs?

I have this friends who is of this particular religion, he would always criticize about other religions and would always call his religion superior. Even if go out in public there are a lot of extremists out there. I just don't see the whole point in dividing people according to religion. why can't people accept the fact that everyone is the same no matter what religion they belong to? BTW,,, I'm Atheist .