> It's not clear to me the difference between "cancel culture" and legitimate outrage.

Legitimate outrage is "I think an opinion you currently hold or thing you currently do is bad, so I'm going to try to cut you off from society until you walk back the opinion or stop doing the thing."

Cancel culture is "I think an opinion you once held or thing you once did is bad, so I'm going to try to cut you off from society forever, even if it wasn't considered bad at the time, and even if you've since walked it back/stopped/apologized."

In a nutshell, cancel culture is refusing to forgive.