You seem to interpret "punishment" as "inflicting pain".
What about denial of privileges or a simple "stand in the corner"? If a kid is being obnoxious right before going to a birthday party, maybe stay home or go late. Or if you're already out, maybe say "this isn't fun anymore" and go home?
I guess you could argue over where the line is between "punishing" and "not rewarding". But I don't think that's a very useful discussion. It's more about how the kid interprets it, and if it's less than they normally get, it feels like a punishment.
If someone is capable of dealing with the consequences of their actions, they are an adult, not a child. A three-year-old could easily make more of a mess trying to clean something. Plus, you need to supervise. The child could easily learn that drawing on walls is a great way to get your attention and play a new "cleanup game".
People who believe in zero punishment have either no experience or a selective memory. Granted, punishment is often overused, but it can be underused, too.
There's a lot of life to experience, but at some point you want to share your life with someone more than just on social media or whatever. Or at least that's how it was for me.
After you've met people around the world and had fine food and hiked tall mountains, it's like, what's next?
Not necessarily marriage and/or kids. But probably some kind of sharing, and marriage and kids are a great way to do that.
If none, does that mean scientific fraud (e.g. adding an impurity intentionally), or is there another credible explanation?