Moral Philosophy/marriage between mother and son and animals
Do you think marriage between mother and son should be legal? And if, in the case the animal is not being hurt, marriage between animals and humans?
Even though some people feel strongly that those things are immoral, if we accept homosexual behaviors because it doesn't hurt anyone, aren't these the same?
I'll answer the one about animals first because it's easier:
The problem obviously is that we don't know what animals think because we cannot communicate with them. So it would be impossible for us and them to negotiate and enter into a marriage.
Legalizing something that is impossible would be pointless.
Now to the inter-generational marriage:
I view marriage as a contract in which two (but why not more?) people agree on sharing responsibilities and obligations and with which they subject themselves to certain laws about alimony, joint property and so on. I don't see it as anything more because it's obvious that love, family and reproduction work very well without marriage.
Therefore, I don't see why mother and son could not enter such a contract. (Obviously only once the son is old enough to consent to it.) Of course it would complicate family law, inheritance law, tax law and have effects on many other legal issues, but that's not a reason to ban it. Maybe it's a reason to abolish the special status of marriage altogether and have the whole thing governed by contract law instead. Then, any two or more people could sign a contract about how they want their relationship to be governed, like they can when they form a company together.
Generally, I don't see how A's feeling that something is immoral can influence a decision between B and C unless there is harm to society. But if B and C want to get married, it doesn't influence A's life at all. Also, B and C and you and me could respond by calling A's objection immoral.