Which laws govern whether or not it is legal or not to post something online? I say that the laws of the jurisdiction where the information is hosted (e.g. Finland) should apply.

Of course if local law forbids you to share information, it is your responsibility to comply.

I'm not an expert in law, and Finnish law especially, but I think it should be illegal to do criminal acts, but it shouldn't be illegal to write and discuss about them.

Murder, arson, theft are illegal, but you can't arres t me for talking about how they are committed.