I don't particularly like HTWFAIP so please don't take this is a canonical reply, but I never read it as an outright prohibition on debate. Rather, it seems to

I don't particularly like HTWFAIP so please don't take this is a canonical reply, but I never read it as an outright prohibition on debate. Rather, it seems to argue that you can disagree but that an effective leader should keep a disagreement from becoming an outright argument. It sounds like a silly distinction, but what if you and I disagree about something. I have two choices. I could: A.) Get incredibly defensive when you disagree, interrupt you constantly, lose my temper and flat out refuse to listen to your ideas. B.) Thank you for disagreeing because we're all on the same team and want to avoid mistakes. Then I'd listen to everything you have to say and work hard to find areas where we agree. And, after I understand your argument, I point out all the areas where you are correct (and especially areas where I am wrong). I'd argue that it's more about learning to disagree respectfully and tamper all the impulses to get defensive and turn it into a series of personal attacks.