I don't tell other people that they are going to hell if they don't believe the way I do. However, Christians tell me that all the time.
I don't see what karma has to do with differing opinions. How do YOU know what "any god" would say to me? YOu don't. You have no more knowledge of "what god wants" than anyone else. Your knowledge of "what god wants" is ZERO, just like everybody else's knowledge.
Many Buddhists are atheists. Or did you not know that?