-Definitely religion and all its various mythological/fantasy ideas of gods, spirits, angels, demons, devils, miracles, spirits worlds, and prophecies of the end times, all foretold through an abundance of really old, archaic books. Add belief in the supernatural as a whole while you're at it.
-Probably slut-shaming, even though I'm usually a proud slut-shamer myself.
-All the hate for homosexuals.
-Probably the death penalty, unfortunately. I don't have any issue with it myself, but there seems to be more and more bleeding-heart individuals that are finding so-called 'hypocrisy' and 'barbarity' in the notion of exercising the death penalty as a form of legal punishment; Makes me wonder if this might end up becoming the consensus view amongst people in the future. Meh.
-We'll no doubt look down on the whole idea of slaughterhouses (and maybe hunting as a sport/fun activity as well) when our technology eventually allows us to create food from animals (hamburgers, fried chicken, chicken sandwiches, hot dogs, etc.) in a laboratory without the need to kill any animals to do it. They're already making progress on this by testing out how well lab-created hamburgers taste compared to the real thing.