There is no true anonymity on the internet. If you’re on it, someone can ultimately track you down. You’d be surprised.
It would probably actually be easy to find out the identity of posters who think they are extra careful. For example, if an FBI agent really wanted to know the identity of Joe1 (made up) and Joe gives no information that helps him and this site is very careful about protecting identity, an FBI agent could simply create an account (or use an existing one) and post a reply to a thread to Joe1 with a link to an ‘article’. That article has a tracking cookie that ends up on Joe1’s computer. In a few days, after Joe1 buys some books off Amazon, checks his phone bill, and orders a Pizza, the FBI would know more about Joe than Joe knows about himself.