First, Eze 23 can hardly be used to note that God thought polygamy was a good idea. The imagery being spoken of is of Judah and Samaria and the point isn't to denote God's polygamous leanings but the idolatry of both nations.P.s. no one is dealing with the actual Biblical texts. For instance, in Ezekial 23 Jehovah uses the imagery of polygyny for Himself. TimV mentioned God gifting David with wives, and also Solomon mentions his wives along with all of his other blessings.
Secondly, the fact that God "gives" wives to David and Solomon needs to be understood as distinguishing between His contol of all things (decree) on the one hand and moral precept on the other. Even as God gave wives to both men (and the patriarchs), one can simply see the historical results of each case and realize that the fruit is never good.
Also, there is a sense in which, when he's condemning David for the taking of Bathsheba that he's telling David that He's never withheld from David anything he asked for and the taking of Bathsheba by such despicable means was a wicked covetousness that wasn't satisfied with the many providential blessings he enjoyed.
As for Solomon, his wives are said to be the reason he's led into idolatry. Were they a blessing from God or a curse? Depending on perspective, it is both.
That all said, one doesn't have to try very hard to "deal" with the fact that polygamy occurred but was not necessarily the intent of marriage when Christ Himself says that Moses permitted it due to the hardness of men's hearts. The patriarchs certainly participated in the substance of the Christian faith as we do but the light they had was significantly less. I think it's instructive to note how polygamy is another way in which God is extremely accomadating to the frailty of flesh. Those of the "moral improvement society" sort might assume that if God never intended for polygamy that he would have just cleaned it up right away and institued a pristine, spiritual religion from the beginning. There's something worth meditating on that God could regulate something that was, as Christ said, a departure from the intent of marriage that, ultimately, pictures Christ and His Church.