I don't think there's a single reaction....it just depends. I can believe that parents of gay children might have something of freak moment, but they just need to get over it. One of my wife's closest friends is very "liberal", but when her daughter came out, she didn't want anyone to know. LOL Her daughter is about 28, is now in a serious relationship, and now her mother has, I guess, had time to get over herself.
Ultimately, unless parents are real freaking weirdos, it's not a long term issue. A very, very close friend of mine got married just about as soon as he was legally allowed to (actually asked me to be best man 💕 ) and there was no hand wringing or anything like that from his family. Of course, he had come out to them shortly after we discussed his sexuality decades ago so maybe that had something to do with it????
Anyway, people need to live their lives in a way that brings them joy. If others have issues with that, It's their issue......not ours.