It's a big thing right now, especially it seems used more by the left. If you did or said anything at all in your past whether it was (A) acceptable at the time but now taboo in today's PC culture or (B) back when you were a dumb and stupid kid that would open your mouth (or hit the keyboard nowadays) before thinking, it comes back to haunt you and puts you on an eternal blacklist, depending on how contrite you are, and whether you are white or a 'person of color' or if you are left leaning or right leaning.
Is it a fad? Is it fair to dig through someone's tweets that they made when they were 15 or 16 years old? Is it right to blacklist a comedian because he told a gay joke back in 1988? This seems to be getting worse, not better.