You don’t remember the early 70s too well do you? A major point of the show is the cultural differences between 1973 and now. Back in the 70s (and 60s and 50s too) “beatin up queers” was a generally accepted hobby for the “tough guy” contingent of our society. A big part of the “lesson learned” is remembering how things were, can’t really know where you are if you don’t know where you’ve been.
What??? Who doesn't know that? What are you talking about? Are you from Iran that you are just learning that beating up people for ANY reason is wrong?