Shariah is the political ideology. It has nothing to do with Islam at all. Do you agree with ISIS/TTP? No, right. Why? Because they are anti-Islam by actions which they practice upon Shariah as their political ideology.
I think you are confused. It is Islam that states Do not marry unbelieving women in Holy Quran. It is suggestion, rule if you will. At the end, it is still your choice whether to marry unbelieving women or not. Only GOD has the rights to judge us, not barbaric conservative culture not you and i nor liberal either.
It is same Islam that also states no coercion in marriage, life and faith. Shariah as political ideology begs to differ.