When your opponent aims to win, at all costs (especially yours), the rules go by the boards. If you obey them, he will not. And if he wins, you can be sure that he will discard them (in your case, at least). The only way to preserve the rules of fair play (constitutionalism, due process, etc.) is to win. And then, by all means, enforce the rules, especially those that punish treachery.