He was doing what he felt he was commanded by God to do., which was totally contrary to accepted mores on polygamy.
Any legitimately logical reading of the same material yields several different takes on the same information, Ray. Like... Joseph did it because he could get away with it. He could snooker his wife, his friends, his followers, the general public and everyone else, so he did. Or... he knew he made the whole thing up with one intention: to get into as many beds as he could, and he never thought he'd get caught (and with unlimited power like he displayed in the Expositor incident, he had good reason to think he was safe). Or... he really didn't care if he got caught or not. He was so certain of his power, anything he said would be accepted as God's word, which would get him off the hook. Or... he honestly thought anything he wanted was what God wanted him to have, including children and other men's wives.
Your reading is only one of many. And it's one of the least likely, to be quite honest.