I'd appreciate correction from someone who knows more about Mouw's views, but I think there may be some confusion here about his views on homosexuality, which he unfortunately wasn't invited to clarify. Mouw does view homosexual sex as contrary to God's purposes. I don't know if he regards homosexual orientation as sinful, but it seems likely enough in some sense. That doesn't imply he sees it as a choice, as some view unchosen inclinations as sinful. (Catholics, Mormons and many others opposed to homosexual behavior do not view the orientation as a sin. The distinction is one many have no patience with, not without some reason, but it's still an important one for understanding the views of others.)
But here's the point. If Mouw does see homosexual orientation as sinful, he seems not to regard the sexual orientation of everyone else as not sinful. He explicitly rejects calling homosexual orientation abnormal while calling the rest normal. He believes none of us is "normal." He is a Calvinist, after all, and keenly attuned to what he regards as a very general spiritual depravity, right alongside divine grace.
That won't satisfy Mouw's critics, of course, but those who want to understand his view may find it helpful.
Some here seem to feel that Mouw is morally wrong to have the beliefs he does, that he isn't only mistaken but shows some moral defect for having those beliefs. I think that's an overly simplistic view relying on several assumptions that may not stand rational scrutiny. In general, moral disagreements don't imply moral defects, even if there is real harm at stake. It should be kept in mind that Mouw also believes real harm is at stake. It is possible for people of good will to disagree about even things this important.
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