Cookies already exist and there is countless leakage (both intentional and unintentional...). Like most things, you are not as private and protected as you seem to think you are. Just because a website is asking you to tell it (which is mostly for compliance, not knowledge) doesn't mean they already know that you said you were 250 years old but your shopping habits suggest you are actually in your 20s and live in Detroit and really enjoy pegging.
Maybe we should add religion and skin color too
To my knowledge, very few nations tie laws or access to that slippery slope fallacy. And parents generally have those same traits (at least while the kid is living with them). So I am not seeing much benefit from this?
And if/when we reach the point where that is the case? Uhm... I don't think companies and software will be given anywhere near as much freedom to say "Sure, we'll comply so that we can be eligible for these contracts" or "No, we won't comply so that we can market ourselves as protecting people"