I think we need to be clear about what kind of punishment is being doled out. Yes, I think any reasonable person will agree that genuinely slapping/giving a beatdown to your kids is not acceptable under any circumstances.
When it comes to something like spanking I think the waters are a bit murkier.
From when I was about 5 to when I was maybe 11 or 12 I got spanked when I really fucked up. My mom or dad would give me one or two hard smacks on the behind. Happened maybe 1-2 times per year at most.
But my parents were also kind and loving people who supported me and never laid a finger on me outside of those moments.
And while those moments were sometimes terrifying as a kid I look back and laugh mostly because I know I was being a little shit.
I haven't decided how I will personally discipline my kids but I don't think spanking should be this crazy taboo subject either.