The slippery slope thing? I don't think that preventing people from expanding their worldview and being more accepting of other people's preference because it might (?) increase the risk of them doing something is illegal is the right way to go.
Just because someone likes something different from the majority does not mean they will start victimizing others because of it. A lot of people imagine hitting their boss or some jerk but they don't do it. The proper way to control and educate should be just that, making people understand it is okay to like whatever you want, but not to the extent of doing something that victimizes others (I don't want to say hurt because people hurt each other all the time, and I don't want to say illegal, because some laws make no sense).
Back on topic, I don't know how much anime you guys watch, but I'm curious what tropes or themes actual anime fans still find unsettling. I ask this because I think I have reached a point where I don't mind anything that would usually shock or turn off others. Don't get me wrong, I still hate some tropes, but that is usually because of over saturation, rather than lack of immunity.