I will leave it to my son to decide who he is most sexually compatible with and who he wishes to spend the rest of his life.
And at 19 and in college, being married is the last thing that he needs.
And you have no problem with other guys treating his little sister the same way?
You are so open minded. It is just in one direction. But hey, way to be a cool dad. Because, you know, values change depending what stage of life you are in. Way to be consistent. Let’s see how the son raises the grandchildren.
While people must ultimately make their own choices, I'm not sure than indifference is the best policy. People look to other people to know if they are doing the right thing or not (it's one of the reasons that people who follow psychopaths do horrible things, they take their lead from the psychopath) and not telling them when you think they are doing wrong hobbles the positive purpose of that instinct. If it wasn't useful for social animals (not only humans) to seek and desire the approval of others, then they wouldn't have that need and we'd be more like cats than dogs, largely indifferent to the feelings and wishes of others.
And, yes, I'm well aware that a parent can be too protective and alienate their children. My stepmother did that with her son, by not approving of his wife, among other things. But I don't buy the "unconditional love and approval" approach, either.
And at 19 and in college, being married is the last thing that he needs.
One can know who they are going to marry before they get married and getting married young isn't necessarily a bad thing. In fact, a friend who found himself having to get married before he finished college wound up finishing college and is in better financial shape than many people I know. He's been married around 20 years and his daughter is now in college. Why is he in good financial shape? Because having a wife and child let him skip the partying and DINK lifestyle that tends to put people into debt without much to show for it. It made him take life seriously.