My state doesn't require rear belts but I still wear mine when sitting in the back and encourage others to do the same. My sibling had a classmate in high school who got thrown out of the rear window while the car was in a roll, crushing and killing him.

It's a little crazy to me that people are perfectly comfortable going 80+ down the freeway with no belts on in the back. Like the two seat backs are enough. It reminds me of the "no smoking sections" in restaurant that were sectioned off by a half wall.