Inspired by this comment, and thinking about how we today look back on (for example) segregation, or the treatment of homosexuals through the last 100 years.
In the year 2120 what do you think human society will look back on and be disgusted to think about?

The big one for me I think will be the treatment of animals, and not just battery farming, but straight up growing them for slaughter: food, clothes, lab-testing, etc. With the nascent industry of 3d-printed/lab-grown meats gaining traction, as well as vegan and vegetarianism on the rise through much of the West, it's not hard to imagine our great-grandchildren being horrified at the thought of their ancestors raising animals just to kill them.

Can be posters, advertisements, videos/films and maybe national/revolutionary anthems/songs.

My favorites so far are:

"Is Colorado in america?" (Basically a US flag with various constitutional rights being
written as violated in the US flag's stripes in Colorado, including the 2nd amendment.)

"Daisy" (Lyndon B. Johnson campaign attack ad, implying that if you do not vote for LBJ, we would have nuclear war.)

Honorary mentions for: Wake up, by the Lincoln project, which has a very similar "these are the stakes" tune for 2020. Mourning in America and We will vote are pretty good too.