Yeah, currently i have the feeling that it still sounds strange. And also that it only became real bad when someone marries of foreign countries out of Israel.
And i think it is not smart to have more than 1 woman (or one man). There is so many temptations in polygamous relationships. Jealousy, hurting, dominating, etc etc.
There is a lot to say about why it is wise to have only one woman (or one man). As you read the Bible you can see that there are a lot of people making big mistakes when they marry more woman.
I dont know wheter it is directly wrong on itself to have more than one wive. Only are the reasons right when you have a second wive?
Currently a lot of man and woman still have polygamy only they dont call it that way. Think of all the dirt that comes on man and womans computers. Yeah, only in the past they were only a little more social and gave food and a place to live for the girls they slept with.
So i believe still today if we look at the Bible that you already commit adultry in your heart if you lust after a woman as Jesus says. Also that you become one with the onces you sleep with in that way.
The reason with David was that he cared for the woman and gave them shelter and food. For some woman a great thing to have. What David reasons were to have these amounts of wives is pretty hard to say. It could be out of lust, competition, showing how a great king he is, out of care for the woman, maybe people gave him their woman all the time to make sure the woman have a life (and that David not even slept with all of them). The woman were nearly as his servants.
Well as we read the new testament i am glad to read that Paul gives elders the advise not to marry more than one woman. And I think it count clearly for everybody. Because i think a lot of people learned from the past, that it makes more trouble than making healthy good relationships.
(Even better not to marry if you dont feel the lust to)
But still I wonder why God did not jugded about these things so much as about these other things.