Perhaps reddit needs a NSFW-like roadblock for special cases like this: Before you can enter the subreddit, you need to acknowledge that everyone is presumed innocent, that reposting things elsewhere can severely harm innocent people, that vigilante justice is bad, etc. Click each checkbox, hit submit, and only then do you get to start reading and participating.
You're absolutely right about vigilante justice, but there's a big difference between that (i.e., playing judge, jury, and executioner) and public evidence-review assistance (i.e., playing forensic investigator).