If he posts his private key online an argument could be made that he is no longer the rightful owner of those funds. You can't just relinquish control of your property and expect the system to baby your carelessness. Statement or not, it's not a good idea to promote irresponsibility.
RE: Daring $EOS Move: Holder of the coin posts their private key on internet -- dares critics to steal their crypto to test security.