Why didn't early Christians allow freedom of Religion among all cultures?

Because people back in the time ignored the idea "Freedom" --- which is by the fact that it is in the Bible (one of the 5 books of Moses, I believe that was Exodus, or Genesis).

Because freedom of religion is a governmental concept, and has nothing to do with the religions themselves. It is enforced by the governments (of course they have it as one of their principles, if not, then as in the former USSR, or currently China, the government acts as they wish toward religion)

The conflict between religions has been a constant since Cain killed Abel.

They did, check your facts. Early Christians promoted their faith but it was always another's choice to accept it or not.

because christians are nothing like their christ they like absolute laws and dont take any crap