It may not be “sworn on a bible true true true” but it could be used to help build up evidence along with other sources or identify people to target for further investigation.

Absolutely shouldn’t be enough on it’s own to be able to get warrants or forces companies like Reddit to give out private information… but there’s be a line somewhere between “someone said they downloaded a movie” and “someone has admitted to committing or planning a horrible violent crime” where law enforcement would be justified in getting warrants. It should follow strict oversight and justification like warrants for “real life” things (I say “should” as in the moral should… no idea how good US laws are around this stuff or how well they are followed”)