King David also sent Bathseba’s husband to the front lines to be killed so he could have her. King David may have been a man after God’s heart but he was still a sinner and God did not approve of him having multiple wives. Polygamy causes jealousy and turmoil in the family as the wives politic for their son to be next in line for the throne. Solomon may have been granted wisdom, but he committed a great sin when he tried to appease his foreign wives by allowing them to build temples to and worship their false gods.
While much of what you said is true, the sins you mention are not the sins of polygamy. In fact, Gods law does not prohibit polygamy and goes even further by providing rules / laws for the treatment of wives (plural). As one example, The Law stated that a man could take another wife as long as he still provided for his first wife (Exo.21:10)
Further, In 2 Samuel 12:7-8, God gave David multiple wives as a blessing.
And Nathan said to David, Thou art the man. Thus saith the Lord God of Israel, I anointed thee king over Israel, and I delivered thee out of the hand of Saul;
8 And I gave thee thy master’s house, and thy master’s wives into thy bosom, and gave thee the house of Israel and of Judah; and if that had been too little, I would moreover have given unto thee such and such things.
9 Wherefore hast thou despised the commandment of the Lord, to do evil in his sight? thou hast killed Uriah the Hittite with the sword, and hast taken his wife to be thy wife, and hast slain him with the sword of the children of Ammon.
This is during King David’s rebuke for killing Uriah and it goes directly to refute your assertion that God never condoned polygamy.
My assertion is that there is far more support in the Bible FOR polygamy than there is for homosexuality which was a sin that called for stoning as punishment.