- Slavery is bad, but Hashem didn't ban it, He regulated it (see start of Parshat Mishpatim).
- Killing our own children is bad, but Hashem didn't ban it, He regulated it (Ben Sorer Umoreh, Ki Tetze).
- Capturing women during war is bad, but Hashem didn't ban it, He regulated it (Eishet Yefat To'ar - see start of Ki Tetze).
I've heard it said that Hashem would have loved to have banned these practices completely, but that wouldn't have had an affect, so instead He, in His infinite wisdom, regulated them in a way that, like a time-release capsule, will work the right moral framework into our system and eventually we would stop these practices altogether.
I've even heard it by sacrifices. "Hashem doesn't particularly want sacrifices, but we really wanted to give Him something, so He made it into a well-regulated mitzva". I've even heard it about eating meat! In our lust for meat, He permitted it, but He doesn't exactly like it...
So, I would like to collect sources of opinions about this general idea. I would be glad to see answers on specifics, but I will accept an answer that deals with the general, or at least most of the specifics above.
One of the questions I would like to answer along the way is how do these ideas gel with the concept that the Torah and its Mitzvot precede creation i.e. the Mitzvot are absolutely Hashem's Ratzon?