Actually, Boissoin did not publish the letter, merely he wrote a letter to the editor. The paper is the one who published it. Should they not be the guilty party here?
Well, actually, NO. The idea behind these kinds of police state laws is to identify individuals with "incorrect" political views so they can be singled out for punishment, the better to strike fear into the rest of the population. If the newspaper bore the burden, it would defeat the hidden (de facto) purpose of the law.