This is a great example on speaking to specific audiences. Conservatives, and I think most Americans as a whole unfortunately, hear "Sharia law" and think it's a codified set of universal Muslim laws that are ass-backward and barbaric.
Sharia law isn't a specific thing. It's a framework for life that varies among Muslim countries/communities. "Sharia law" means something very different to a Muslim in SE Asia vs the Middle East, and obvious it's diverse within that. The law aspect is also a weird lost-in-translation because we're talking about a religion/cultures/ethnicities that often don't have independent legal systems.
The Trump campaign attempted to use this triggering phrase and it's rather embarrassing.
Some decent reading:
Pew Research ... Most Muslims want Sharia law... but nobody agrees on what that is. - Skeptical Science
In Defense of Sharia Law | The National Interest
Why is Islam so different in different countries?
This is a lot like saying that Christians want their legal system to based on a literal interpret ion of scripture, only thing is there is no literal interpretation... Everyone disagrees!
Whether or not their is agreement on everything between biblical fundamentalists, its novel to start arguing that there is nothing that can be gleaned from a person supporting that. It's this constantly shifting argument with citations that makes everyone suspicious that the real criteria is "it's smart and good if a Democrat did it."
Even if their weren't, the article Mr Khan wrote was on why he thought one particular school of Sharia could be treated as authentic.
But you can't have it both ways. If supporting Sharia Law could mean a whole host of benign and even positive things, then you can't say that it is "attacking" or "insulting" to point out that someone supports it.
At least insofar as it makes no sense to advocate for it as the basis for a legal system, to cite a specific school of it, and then to claim it has no meaning-- "well then why wasn't your article incoherent?!"
The whole argument is over-reductionist. The overwhelming majority of Muslims are peaceful people that want the same things everyone else does, but that doesn't mean that Islam is a religion that just teaches peace and tolerance between all people.
I mean goodness gracious, we call out Christians in this country for their sexist and homophobic positions all the time. Why should Islam meet modern standards, top to bottom, as a matter of indisputable fact?