1) Artificial scarcity - like Wordle or a NYTimes cover photo, there's only one per day. This focuses attention to one topic at a time.
2) Before/after polling. The audience is polled initially and then asked if they've changed their mind after a while reading arguments. The winner is the debate that changes the most minds.
https://en.wikiversity.org/wiki/Should_animal_testing_be_leg...
https://idebate.org/debatabase/environment-animals-philosoph...
What's the difference vs a reddit poll?