>We have overwhelming evidence that corporal punishment is harmful in general, and very harmful for kids.
This is false. The evidence is not overwhelming; it's actually extremely poor quality. And the research question is one of the most difficult to resolve in social science. I wrote on this here: https://wyclif.substack.com/p/the-academic-literature-on-sma.... See also this guy: https://scholar.google.co.uk/citations?hl=en&user=2HtqmZ0AAA...
You might not have noticed what you've done here, but you've not only agreed to corporal punishment for children but also for harsher corporal punishment for criminals across the board. Read the whole conversation chain and reflect on how bad the optics are. There is a reason why your stance is unpopular.
"Spanking looks like an 8/10 on the subjective harmful scale, but actually on the objective harmful scale its closer to a 3/10. We must rectify the bad reputation of spanking!" is not the type of motivation that should drive pedagogy research.
There will never be proper studies with control groups to test exactly how harmful beating children is, so this is an unrealistic standard to expect. Given this context, the person you're responding to is correct: we have overwhelming evidence that corporal punishment is harmful in general and very harmful for children.