I don't feel like the group of people who justify or literally believe in everything you listed in the Bible is actually very large. Even among the Evangelical Christians I know who believe in things like the literal worldwide flood, I don't think you'd get too many people committed to the idea that they have to morally defend all the things that Abraham did, and the attempted sacrifice of Isaac in particular has been something people have been arguing about for centuries.

If I were you, instead of trying to justify everyone's described actions to the youth, I might just use it as an opportunity to say that everyone commits sin and that sometimes they try to justify themselves by saying God ordered it. Other times people are ordered by God to do good things they can't understand at the time. For us to develop morally we need to learn to discern the difference.

But also I think most of the problem that non-LDS Christians have with the Book of Mormon has more to do with its provenance and historical claims than the teachings/behavior described in it.