I think the argument is more around it being illegal so as to not be forced into playing "the bad guy". It's hard to prevent a level of entitlement and resentment if those less well parented have full access. If nobody is allowed then there's no parental friction at all.
Its unfortunate that the application of this rule is being performed at the software level via ad-hoc age verification as opposed to the device level (e.g. smartphones themselves). However that might require the rigimirole of the state forcibly confiscating smartphones from minors or worrying nepalise outcomes.
But it's not playing the bad guy. It's playing the good guy.
I'm saying hold parent's accountable for their children's online behavior and for their protection online, not companies (who want to profit off the kids, perverse incentive) or governments (who can barely be trusted to do this even if this was the only goal). For example if your kid starts making revenge CP of their classmates, and the parent could have reasonably mitigated or known about it, I think the parent absolutely should be held responsible.
Don't punish the rest of the web for crappy parenting and crappy incentives by companies/govts.