I saw an after school special called "What If I'm Gay?" from the 80s that was surprisingly progressive and didn't lean on stereotypes or tropes. My elementary PE teacher was an LGBT+ activist, and we had at least one openly LGBT+ speaker at a school assembly who spoke about acceptance, and I grew up in a small conservative town.

Even Nirvana wrote in the liner notes for one of their albums that sexists and homophobes shouldn't buy their records or come to their shows.

I didn't know a lot of openly trans people back then, but that's because many people didn't feel safe coming out. Regardless, I can't imagine having responded with the brand of ignorance and hate we were actively pushing back against.

With that being said, LGBTphobia was certainly commonplace back then, but as you said, there was no excuse. People knew better, but they participated in it anyway.