My personal instinct is that there are things that are detestable, period. You shouldn't do them, regardless of whether they came before or after God spoke a law against something. I doubt that child sacrifice was perfectly okay to God until he spoke against it. Was there a law against murder before Cain?
Your subject heading of whether to "praise people" raises a question about what the purpose of the Old Testament "heroes" are about. Yes, there is one view, a "Theology of Glory" kind of view, where the OT heroes are moral examples to be followed by us with great effort. Here, blind obedience to God, no matter how brutal or politically incorrect, would be praised. Our moving towards God means doing more things like Abraham.
In another view, the OT stories remind us of how much God loves bad people, that even in the OT, God's favor is not sent to the deserving. It is a gift, not a wage. In this second view, the purpose of the story of Abraham has to do with God providing:God will provide" the sacrifice, says Abraham. "God who makes the demands, meets the demands," said Tullian Tchividjian in a sermon on this story. It is to point to a sacrificial substitute.
Tullian Tchividjian has a sermon on this entitled, "In The Beginning, ... Grace Part 9". http://www.crpc.org/media/sermon/in-the-beginning---grace---part-9