This particular example is not even difficult to deduct from some pretty basic axioms of morality, mainly that disadvantaging someone on the basis of their sex is wrong and that people should have personal freedom so long as it doesn't infringe on the rights of others.
A lot of those women who cover themselves from head to toe believe it's the right thing to do, and also believe that forcing other women to do the same is the right thing to do.
That's his point. What you believe is right and wrong is not the central basis for morality.
I think this ‘provocative’ comment has forgotten the human element in this.
They do so because they believe it is right.
This gets so overblown especially by people who benefit from this idea being spread, while the truth is that the amount of people who actually do want Sharia is very low and the amount of people who are actually "marching" to get it implemented is even lower.