This is intellectual sparring. We're not testing your vocabulary. We're testing your mental flexibility.
You'll learn to see any issue from both sides, stop freezing when someone unexpectedly agrees with you, and keep any conversation alive - even the tricky ones. Sample thesis: "University degrees are becoming obsolete." Love your degree? Great. Prove the opposite in one minute. No preparation.
Takeaway: Spontaneity, quick thinking, and the courage to say "Let me play devil's advocate here..." with a straight face.