So if I put on a nazi blog that said something akin to um I’m going to kill all of you… Given I don’t know who they are beside username and where they are at would I be arrested? How is that different from what the 20 year old did? He was just more specific as far as I can tell.
Uttering threats is a crime. Libel and slander are crimes. Surprisingly to some, there are in fact things you can say (or write) that are illegal. Being charged for committing crimes is by definition not precrime. Also, they may be out to get you, but if you don’t know enough about the law to even be sure if you’re breaking it or not, you will make it very easy for them to do so.