The very term "debate" has antagonistic nuances. That's why you have "opponents" in a debate. It's all about persuading the other side of the validity of your viewpoint. Not about learning anything. It's information "push" - no way to get at objective results, even when one side clearly "wins". More about showing off mental trickery (as opposed to dexterity) and stubbornness (as opposed to steadfastness). Useless, stupid and wasteful of time and effort.

Whereas a "discussion" has "participants" - who may have a starting point of view, but may well end up with different ones. It aims to get at the truth, and requires an open mind. It's information sharing, push as well as pull - much more condusive to objective results. Not as much fun to watch by a society geared towards confrontation, winners and losers, playground-nyah-nya-teasers, but hey, you get what you ask for.