There are several issues brought up in the opening post. First of all, the main point, if you are going to have freedom of speech, that means you are going to allow unpleasant things to be said. Otherwise, "freedom of speech" isn't really freedom of speech at all.
Now, if they actually are planning illegal activities online, then they can be prosecuted for that. And if they [stupidly] post proof of illegal actions that they have taken in the past, then that can be used as evidence against them for the purposes of prosecution.
Now, if they actually are planning illegal activities online, then they can be prosecuted for that. And if they [stupidly] post proof of illegal actions that they have taken in the past, then that can be used as evidence against them for the purposes of prosecution.
"A wise man ... proportions his belief to the evidence."
— David Hume, An Enquiry Concerning Human Understanding, Section X, Part I.
