I dunno. As you said some of this might be taste, and it isn't the case that we would all like every taste if we gave it a chance. I hate sweet food (ironically, since I love sweet music) and I don't need more ice cream and cake to know I don't like sweet food.
My experience with my friend on mushrooms gave me the impression that no amount of exposure would get him to like a sentimental pop sound. He was in the vulnerable state where I might have thought he would give new music a chance. But instead, he rejected it with an honest answer, and it revealed to me something about his inner persona: feeling sentimental emotions clashes with who he is at his core and the feelings he wants to feel. I think there's something about a typical macho male personality that doesn't want to experience vulnerability or sentimentality by definition, and whether it is nature/nurture I do think it is at the core of what their personal identity is.
As they say, there's no accounting for taste. While experiences may have guided people into particular tastes (particularly in their youth).... it doesn't mean that continued exposure to all tastes will eventually create a fondness for all of them. But as you said, taste isn't firmly set in stone either. It's pretty mysterious.
I think a good amount also has to do what what we grow up with as well. So if you're never really exposed to something that sounds sweet, then there could be a chance you'd react to it negatively. It's just that I personally find it strange when people just don't like a genre without really giving it a shot.
Being black. I know so many dudes who usually listen to hip hop, the hard stuff that most people would associate with the genre if they don't listen to it too often. That being said, those same dudes will know nearly every lyric to every classic R&B song that our parents and those around us grew up listening to, and there is nothing "hard" about the vast majority of those songs. They're very emotional and usually lovey dovey.
These songs are way less "manly" than some random pop song sang by Taylor Swift or whoever. Plus I haven't read through the whole thread, but why aren't people accounting for music like that?
I feel as if it's just a vocal minority that's against certain types of music, because in my experience, the majority has plenty of variety in taste.
Plus while I don't mind sad sounding sounds at all, I personally don't like listening to sad songs just for the sake of being sad. I only bring this up because I know a few people who do, and I just don't understand it lol.