What would be more meaningful: certifications that act as abstractions for complex problems. Organic kind of acts like this already, and of course there are multiple federal certs for electronics. Having a functioning regulatory system as well as a working civil law system also help.
That's a completely actionable warning. Don't eat the contents of the battery of your cell phone.
Or how about "This carpet contains formeldahyde, which is known to cause birth defects in pregnant women. Limit exposure to this carpet for a few days after installation."
That's a good warning. That tells me what I need to know, what the risks are, and how to mitigate it.
We have to find a middle ground between "has chemicals that may cause cancer" and "a hundred specific chemicals in X quantities that may cause cancer." Abstraction is very necessary as a pragmatic solution, even if full disclosure makes sense as an ideal.
Heck, most places are just doing CYA, they have no idea what specific lists of chemicals their contractors use. For the IoT case, no one has any idea how their devices can be exploited, and merely admit the possibility of exploitation. But that is another issue.
If it is only harmful if ingested you know not to give it to your toddler. If it gives off toxic fumes while burning, well, stay away if you made a fire mistake. etc. The warning itself is pretty useless as it is.
Therefore no people should be allowed to know?
For what it's worth, I'm not in favour of California's labelling requirements either. But just because something is meaningless to the majority of the population doesn't mean it's meaningless to the entire population. And it is specifically the population that is interested in knowing it that finds it least meaningless!