What does the Bible say about adoption by same-sex couples?

Leviticus 20:13: "If a man also lie with mankind, as he lieth with a woman, both of them have committed an abomination: they shall surely be put to death; their blood shall be upon them."

This is the same book that forbids cotton/poly blend shirts (Leviticus 22:11: "Thou shalt not wear a garment of divers sorts, as of woollen and linen together"), of course, so strictly speaking you don't get to pick and choose which of the forbidden practices you condemn outright and which you say "yeah, well, they didn't have polyester then, so I'm sure it's okay" about.

The one justification Christians have for insisting on the one but not the other is that in the New Testament there's a passage (1 Corinthians 6) that basically says "we're not under the law anymore, so we can do nearly anything we like, but thesethings are still sins," one of which is "sexual immorality" (and homosexual acts between men are called out specifically).