the fact that writing is speech. any restriction on what I can or cannot write is a violation of freedom of speech, whether someone has previously written it or not.
in this respect I believe that the copyright clause and 1st amendment are contradictory
They are contradictory in the sense that copyright law limits the scope of legal "speech". But that does not imply a nonsensical position. You may quote copyrighted works for legitimate purposes of criticism or fair use. You may not "express" a complete reproduction of a substantial amount of material in a way that deprives the original person of profits.
Copyright law is not intended to be abused as it is on YouTube and other social media, where people get videos taken down because they had an image from within a game. That's just stupid copyright trolling and would not stand up in court.