Idk man, why put it? I agree, I down voted the proposal since it was useless. Didn't go mad posting about it tho.
I understood from the beginning that you are trying to make a "slippery slope" point, but this is open source, each change should be evaluated as is, with what it implies. A local field that isn't being used in anything doesn't condition users or Devs to anything that will then make them accommodated and easier to approve an actual invasive feature.
I will agree with the slippery slope argument when they propose a feature that is minimally invasive. This was both useless and 0 invasive.
Edit: actually no, this feature wasn't useless overall. It was useless for age verification, but great for parental control. The moment a kid doesn't have root access to the computer, a parent can put whatever age to block the kid from whatever features the parent wants to block them from. Think about it, self enforcing age verification doesn't give power to governments, it gives it to the root user of the computer, aka parents. It's something that actually works.