“You’re Not Going To Agree, So Let’s End This”
If you feel a debate has a reasonable chance of influencing the minds of participants, then let it continue.
If you feel a debate is introducing new, high-quality, information others might find useful to inform their opinion, then let it continue.
If you feel participants are simply repeating themselves, flinging selected statistics at each other, and drifting further apart, it’s probably time to step in and lock the discussion (with a short explanation why).
Sure, allowing provocative discussions to continue endlessly looks good on engagement metrics. But that’s an extremely short-term approach. Once people associate a community as a place where they spend a lot of time without gaining much value, they stop visiting.