Your premise is faulty. The aim of debate isn't to foster people who form their own opinions any more than baseball is designed to foster people who can reliably strike fast-moving objects out of the air to a stick. It's a sport, it has rules, and it rewards tactics and strategies devised within those rules. Read Patrick McKenzie about this; he's written a bunch about how competitive debate was unintelligible to outsiders as far back as the 1990s.