Tallg

I am sure you have heard of the khawarij. They are a group of muslims that you will see crying. Even the sahaba (the best of their generation) used to see them and think they were better then them because of their piety and crying during prayers.

So why did the Prophet Mohammad say that if you see these people "kill them where ever you find them?"

Because they make a persons mistakes (sins) as something that takes them out of the fold of Islam.

This is very different then a persons Islamic belief (aqueedah)that takes them out of the fold of Islam.