The fact that Reddit comments are admissible in a court sounds insane to me. I can't believe people actually take Reddit that seriously. It's like taking preschoolers yelling at each other seriously, but with anonymity thrown in. The fact that adults can take it seriously enough to use it in court cases is crazy.
Just because you don't know the reddit user in real life doesn't mean other people don't know each other in real life. If someone says they're going to kill someone for a comment, and then that user ends up dead, I don't see why it would be shocking that might be used as evidence in a court case.
It was a pretty common occurrence on Twitter back when people posted their gang crap everywhere.