I agree with literally everyone who thinks this is pointless and probably malignant. The problem isn't the visibility or the fact that weird stuff "exists" on the internet. The problem is advertisers "showing" it to people who didn't go looking for it. Ads and algorithms that decide what a person to see are 99.8% of this actual problem, and meta lobbying for something like this is just obvious self-interest to absolve them from any liability for showing kids damaging material, and to hit 2 birds with one stone, they get more PII to add to their "anonymized" aggregate data.

No good will come from this for the consumer. Websites are suddenly all going to start accurately reporting their content rating, especially ancient documents that have been "online" since before css and javascript were a thing. The only ones that will be implementing these checks will be adtech people that shouldn't have it in the first place. Letting out of touch geriatrics make tech policy decisions in a time when the bleeding edge is moving faster than ever is going to be disastrous for generations to come.