If we focus only on high school debate for a minute (I have participated in and coached high school teams), the point is to teach kids critical thinking. When freshmen show up to debate for the first time, it might surprise you how bad they are at putting together coherent arguments. You don't get to make it to the top of the league in debate without learning critical thinking. In order to get to the "obnoxious and inane" parts of debate, you must first succeed at the point of debate (to teach critical thinking and argument). So, I'd say high school debate does a great job at what it is meant for.

Edit: Moving from a long-form rant about something that a freshman barely understands to philosophical minutia that lead to nuclear war takes a significant amount of learning. And that learning is worthwhile.