Sciency types make fun of academic philosophy, often with reason. But sometimes it really does seem like conceptual work has to be done before we know what we are disagreeing about. So it is here. No one can really dispute that Islam-as-historical-phenomenon involves some unjustifiable violence and sexist oppression. On the other hand, the same can be said of Christianity and Buddhism. Scientific materialists have to explain away Stalin and Mao. Since the decision in WIC Radio v. Simpson, I can even point out that New-Agey Nietzschean post-Christians have some explaining to do.
And, at least in the context of Christianity, I can cite text. In addition to Augustine and Aquinas on religious coercion, there is the OT. Joshua made Mohammed look like a wimp. Opening randomly, I see Josuha 8:24-29:
When Israel had finished killing all the men of Ai in the fields and in the desert where they had chased them, and when every one of them had been put to the sword, all the Israelites returned to Ai and killed those who were in it. Twelve thousand men and women fell that day—all the people of Ai. For Joshua did not draw back the hand that held out his javelin until he had destroyed all who lived in Ai. But Israel did carry off for themselves the livestock and plunder of this city, as the LORD had instructed Joshua.
So Joshua burned Ai and made it a permanent heap of ruins, a desolate place to this day.
So what claim is "anti-realist" making about Islam?
As for Marnie, she claims that the law requires that the person who asserts a claim prove it. That is true -- at trial. But lawyers also have processes for striking pleadings or for giving summary judgment, where the person disputing the claim has to show that it is without merit. Ms. Donohue did not have to prove that her ginger beer had a snail in it, but only that it wasn't crazy to sue if it did. And it seems to me that if you are going to say that certain claims should be subject to legal sanction, you face as big a hurdle.
It also strikes me that one concept that seems completely inconsistent with the Qu'ran is invoking a secular norm of religious equality to prevent examination of the truth claims of religious practices. The idolators the Prophet railed against did not mind the worship of Allah -- they just thought Al-lat and the Sun and Moon should be respected as well. Certainly, no one should be permitted to offend their worshippers. It is easy to imagine the Meccan Human Rights Tribunal levying a stiff fine for aggressive monotheism.