The Qur’an says in in verse 256 of Sooratu-l-Baqarah (soorah 2): ( لا إكراه في الدّين ), laa ikraaha fi-d-deen, which means, “There is no compulsion in religion.”
Why? The Qur’an explains further in the same verse: ( قد تّبيّن الرّشد من الغيّ ), qad ttabayyana-r-rushdu mina-l-ghayy, which is translated as: “Truth stands out clear from error.”
Thus, because the truth is clear, there is no need to force people in matters religious: they all know better, and unto each his/her own to work out his/her own salvation, as it were.
So…whence shariah law and its enforcement of draconian penalties on transgressors?
Well, the fact the the common interpretation of 2:256 is not entirely correct. There is no compulsion in forcing people into the religion – for if they reject it, they do so knowing clearly well that they are wrong – but once a Muslim, the needs and obligations of the Muslim community takes precedence. Thus, any endangerment thereof is severely punished, as is any non-compliance. So, Muhammad should have said, “There is no compulsion in converting others to the religion, but once you’re a Muslim all bets are off.”