You are absolutely correct in what you are quoting, but I still go back to 1 Kings 15:4, which obviously only points out the matter of Uriah the Hittite. If God is against polygyny, wouldn’t He have pointed it out here?
I can reason it this way, though keep in mind it is me talking not the Bible. In the matter of the census, David didn’t disobey a command, though he sinned. In the matter of Uriah the Hittite, he committed adultery and murder, both of which are violations of the Lord’s commands. If this is true, the we can conclude that polygyny is not a violation of the Lord’s commands. Whether that line of reasoning is correct or not is up to debate, I think, but the fact is that The Lord has not issued a command against polygyny except, depending on your understanding of the corresponding verses in the New Testament, for leaders of the church. Don’t you think if it was so sinful there would have been a clear command about it?
"For this reason a man shall leave his father and mother and be joined to his wife; and they shall become one flesh."
Please note the word of God uses the singular form wife, (not wives). Just because God allowed polygamy in Old Testament, doesn't mean He approved of it.
Also note what Paul says in 1 Corinthians 7:2:
"But because of immoralities, each man is to have his own wife, and each woman to have her own husband."
Please note once again, Paul uses the singular form wife, not wives in this text. Clearly, God's will in one man and one woman in marriage.
The world can do as it pleases, and justify what it wishes with regard to moral law; but you cannot justify polygamy via God's word; which in the end, all men will answer to, and be judged by.
1 Satan rose up against Israel and incited David to take a census of Israel. 2 So David said to Joab and the commanders of the troops, “Go and count the Israelites from Beersheba to Dan. Then report back to me so that I may know how many there are.”
3 But Joab replied, “May the Lord multiply his troops a hundred times over. My lord the king, are they not all my lord’s subjects? Why does my lord want to do this? Why should he bring guilt on Israel?”
4 The king’s word, however, overruled Joab; so Joab left and went throughout Israel and then came back to Jerusalem. 5 Joab reported the number of the fighting men to David: In all Israel there were one million one hundred thousand men who could handle a sword, including four hundred and seventy thousand in Judah.
6 But Joab did not include Levi and Benjamin in the numbering, because the king’s command was repulsive to him. 7 This command was also evil in the sight of God; so he punished Israel.
8 Then David said to God, “I have sinned greatly by doing this. Now, I beg you, take away the guilt of your servant. I have done a very foolish thing.”
9 The Lord said to Gad, David’s seer, 10 “Go and tell David, ‘This is what the Lord says: I am giving you three options. Choose one of them for me to carry out against you.’”
I find it VERY hard to believe that a person can 'sin' withOUT breaking a command of GOD.