I think the uproar comes because the well is already poisoned. People are already trained to respond with an outburst of anger to any law that mentions the age of the user, and will find excuses to rationalize that outburst, even when the law isn't that bad.
I mean, "compelled speech"? Really? That's people's argument? This is about as bad as the government compelling you to write a copyright notice.
Compelled speech is bad and it’s something we don’t do, at all. All kinds of bad things come with compelled speech. Mandatory loyalty oaths, erosion of the fifth amendment, compelled work to weaken encryption, etc.
The well should be poisoned. The whole idea is poison.