Given your lack of history of violent revolution (I'm assuming), I'd guess it's because you look like a hypocrite for sitting behind a keyboard and telling others to do something you're not willing to do yourself.

People protesting (legally and peacefully) have been targeted based on social media accounts.

Yes, this is bad. People should not be targeted because of what they wrote.

This is closing the gap to allow similar fascist behavior on an even more personal level.

On a personal level.

Yeah, that would be bad. Kind of like a targeted harassment campaign of a person because of what they wrote.

It's one thing to be against age verification or software that does age verification or platforms that require age verification. That isn't what is happening here.

That fight is political, this is an engineering problem.

You could argue that this enables age verification, it doesn't. Age verification software can exist without this field, it could store your birthdate in .config/EvilAgeVerificationApp/userinfo.txt.

The field is an optional entry, systemd doesn't require it or verify it. It is simply the most logical place, from an engineering perspective, to store the data.