Poor = Disposable
It's always been that way
Adoption is a court process that's a lot more involved and public than a marriage license. For gay marriages, consanguinity issues are irrelevant because there will be no offspring. Think father-son and mother-daughter.
What is to stop an extremely wealthy man from "marrying" his son… or grandson? When man dies, "spouse" owns everything as sole surviving spouse. Rinse and repeat, elimination of estate taxes. This can be done very quietly and until the death, who is to know?