"I don't understand the progressive left.."
WALLe, excellent question.  At the risk of collecting scowls I'll  suggest some  answers--
As  a  liberal I do find some of the practices of Sharia objectionable, and if someone were actually trying to force Sharia on us I'd be out in the streets protesting with you.  However, as no such threat exists, I'd say the American thing to do when it comes to religion is "live and let live."
Not all Islamic societies enforce Sharia or similar values, though Saudi Arabia, Trump's current friend, unfortunately does.
More important, one can find similar teachings  in the Old Testament used by Christians or the similar Tanakh used by Jews.  Some horrific stuff-- stoning of adulterers, wayward sons and non-believers; God's command to trick another tribe's men into circumcision so they could slaughter them, etc.... 
But such  fundamentalist abominations are not  practiced by most America's Jews and Christians, just as with most America's Muslims today.