And as it is, not every person may marry. Sisters cannot legally marry their brothers. . .so it’s not as though you can say that ‘any man’ may marry ‘any woman’. There are already limits in place because it is recognized that there are some ‘degrees’ or relationships that preclude marriage.
You’re assuming that incest is going to remain illegal forever. That is not my view. With medical progress, it will be possible to identify potentially defective embryos due to consanguinity and abort them. The traditional motives for the prohibition of incest (endogamy and religion) will loose force in rich countries and eventually the principle that “two consenting adults can do whatever they want” will prevail.
However, the Church will never accept abortion, gay marriage, incest, polygamy, etc. What I think is that societies accepting those things openly will, in due course (2, 3, 4 hundred years?), loose vitality and be substituted by younger, more dynamic people that do not view those things as fundamental rights. The point, in the end, is that those practices are fundamentally flawed from a society viewpoint. They all tend to hamper its vitality and potential. It is of no importance that we Catholics are called “bigots” or “homophobes”. Those are just tags that people put to other people. Things are just the way they are and these practices are dynamically inconsistent because they tend to rarefy their practitioners.
As a side note, it is instructive to observe that, while the view that some races are inferior to others, or women are inferior to men, or people can be held captive, etc. have been condemned by the Church from the very beginning, abortion, sodomy (not homosexuality), incest, etc. have been rejected from the outset by Christianity.
Et pour cause… You cannot be discriminated by things that you have to choice upon: your race, your gender, the society you’re born in. On top of that, accepting all races as fundamentally equal, dignifying women, and freeing people are progressive actions that unleash the potential of people.
In contrast, you can choose not to abort, not to practice sodomy (even if you have homosexual tendencies - that’s no sin), not to have sex with relatives, etc.