When I say "I don't know" I am actually saying that I can't offer an adequate answer. I posted in another thread about God’s wisdom is not always the same as our wisdom. I’ve gone most of my life not trusting God, and I can assure, doing that didn’t work out too well for me.
We will not always know all of the reasons for why God forbids certain things and allows others. Sometimes it’s obvious, other times—it’s not so obvious. Philosophies, psychology, sociology all have limits; and they are certainly limited in the understanding between God and His creation.
Many here have made some compelling arguments. But as strong as they are, none of them have convinced me not to trust what I think God has said on the issue.