Well, these are apparently mainstream views among muslims, at least according to Jonathan AC Brown, who serves as director of the Alwaleed bin Talal Center for Muslim-Christian Understanding at Georgetown and who delivered his views in a recent lecture. His argument is that slavery, for example, was practiced by Mohammed himself. From the link:
“The Prophet of God had slaves. He had slaves. There’s no denying that,” he told a man during the Q&A session. “Was he — are you more morally mature than the Prophet of God? No, you’re not. I’ll answer your question for you.”To be fair, it doesn't seem that Johnson, who is a white convert to Islam, was actually calling for, or promoting, any of these things. Rather he was defending Islam, a religion in which such practices are permissible. How many muslims agree with him is hard to say, but even so, if a Klansman defended a worldview which permitted or tolerated slavery, forced sex, or concubinage he would be rightly excoriated for it, no matter how many people in the larger culture he represented.
He also questioned what it meant to give “consent” to sex and to be autonomous, all in an attempt to defend Islam.
“It’s very hard to have this discussion because we think of, let’s say in the modern United States, the sine qua non of morally correct sex is consent. We think of people as autonomous agents. Everybody’s an autonomous agent and it’s the consent of that autonomous agent that makes a sexual action acceptable,” he said.
“If you take away the consent element, then everyone starts flipping out,” Brown continued, adding: “We fetishize the idea of autonomy to the extent that we forget, again who’s really free? Are we really autonomous people?”
It doesn't follow from the fact that we are a culturally diverse society that views which are unacceptable when endorsed by one group should be tolerated when endorsed by another. Why, then, do some wish to make an exception for muslims?