A big red flag here in the false prophet area is Joseph Smith attempting to re-institute Polygamy. And clearly something the Apostles of Jesus were teaching against when they were instructing the Church of Jesus the Christ:
1 Timothy 3:2
"A bishop then must be blameless, the husband of one wife..."
It is true that God told the apostles that a bishop had to be the husband of one wife. Is that because some good men had more than 1 wife at that time?
You knew it was culturally OK for a Jew at that time to have more than 1 wife? Right? It was written in their law.
However, Jesus was creating a whole new testament and he re-instigated , the law of men being married to 1 wife. So from the time of Moses to the time of Jesus it was institutionally and culturally OK to have more than 1 wife. But from the time of Jesus to JS it was institutionally and a cultural norm for men to be married to 1 wife.
Does this mean that now God had boxed himself into a corner, and did not dare to institute plural marriage again? Heavens no, God does not get to be boxed in by you or a bible, or anything. If God wishes to institute plural marriage again for a specific reason and that is wisdom unto him, he gets to without a whimper from anyone that he is going against some norm.
Remember when Peter was shown pieces of unclean meat in a dream and the Lord said to eat? Well, you know the norm in Peters day had been in affect for 1400 years, God had said not to eat certain meats, and so when God said eat, Peter objected. What did God say to him? Do you remember? God said whatever I command you to eat, you eat, even unclean meat is clean to you if I command you to eat it.
This dream was a precursor for baptizing a gentile, which for 1400 years God had said it was taboo to Jews. Now God said they were clean and were to have communion with the Jews and be a part of his new church for Jews and gentiles and anyone that objected or rejected this command would be out of his kingdom. Wow, what a massive change to the norm.
So if God says that it is OK again to practice plural marriage, are you going to object and reject God's work because at one time 2000 years ago he said he wanted men to be married to only 1 wife. You might, but JS after struggling like Peter, did what the Lord commanded and in all of it, God counted his plural marriages as righteousness, and not adulterous, because he had commanded it to be done.
Yes, red flag, but after studying it out, take the red flag down. Since God commanded it, it is good.