I agree with you, but then the implication becomes, "any platform that allows user content must scan all content posted or uploaded by the user to determine if any of it suggests they are a minor".

I adds a bit of burden to all sites under the threat of civil penalties. Say I own a site that allows user posts like HN. If someone mentions they're in grade school in any post and later starts receiving links to adult sites in their DMs, now I'm liable.