From Reddit, a question that yielded a number of thought provoking answers:
So many of our grandparents were racist, and some of our parents are homophobes. Which of our own closely held beliefs will our own children and grandchildren by appalled by?
Phil Dhingra collected some of his favorite answers.
That drugs were illegal
Eating meat
Monogamy (or anti-polygamy)
Imprisonment vs. rehabilitation
Attitudes about human treatment of animals is something that will likely change in my lifetime. At some point domestication and consumption will move from something that we do because our ancestors did to something that just doesn't fit into modern society. In a cultural sense, humans don't belong to the animal kingdom anymore; we're not normal predators that need to kill animals to survive. Soon we'll have the technology to grow enough meat in factories to satisfy even the most hardcore meat-eaters. Once this happens, it will be difficult to justify the continued imprisionment and slaughter of cows, pigs, chickens, and the like simply so that we can eat what we like rather than what we need to survive.