The penalty is death. It defines a lot of that religion. Deviations and change are not allowed. Conformity is enforced. One tenant of Islam is that there will be no prophets after Mohammad, so nothing can change or be updated. It's all in scripture, set in stone. Islam and Christianity have their good points and bad, but Islam is a dead end because humanity is in a rapidly changing world. Islam is good for a feudal society very like the Old Testament was about, but it is not appropriate to changes after that and the West is past the feudal society.