Exactly. If they couldn't tell the difference, then how could they know which content to seek out for their own enjoyment. It might not affect them much, if at all anymore, but they know what 'it' looks like.

Can you imagine them watching a cute cat video over and over and wondering why they aren't getting the rush they must feel when watching gore.

I remember in the early days of the internet, i clicked a link on a forum and ended up watching a video of some guy being decapitated. I have never forgotten that image, 20+ years later, and i know i would be checking into a mental hospital if i had the job these facebook staff have had to do. But there are people who like this sort of stuff, and its not because they have forgotten what decapitation looks like.