I have yet to see where it says in the scriptures that polygamy is a sin btw. I'm looking and haven't found that reference. However homosexuality is clearly outlined as a sin.
And IMO, polygamy isn't for everyone. It's something I believe very few can handle. And while Abraham, Isaac, Jacob and Moses all had their issues, they were all very special men who I believe did their very best to treat their wives as best they can. I'm sure there were days where the wives had to remind him to take out the trash, bless the children or even repair the home.
Even though the church doesn't practice this today, it's still part of the doctrine. It's important to remember that we're always growing and learning more about God and the gospel. This is part of our training for the eternities.