Underage drinking is a social problem.

The issue isn't social media is bad, the issue is that social media has no effective moderation. If an adult is hanging out at the park talking to minors, thats easy to spot and correct. there is a strong social pressure to not let that happen.

The problem is when moving to chat, not only is a mobile private to the child, there are no safe mechanisms to allow parents to "spot the nonce". Moreover the kid has no real way of knowing they are adults until it's too late.

Its a difficult problem, doing nothing is going to ruin a generation (or already has), doing it half arsed is going to undermine privacy and not solve the problem.