Carcinogens are very, very tricky to study rigorously.
I joke with my work buddies: "Thousands of peer-reviewed studies have shown that research causes cancer in laboratory animals." (We do research for a living.)
Not all carcinogens have been identified, by a huge margin, and some of the worst are noticeably carcinogenic in quantities that modern instruments are unable to detect. In order to discover that, researchers had to make careful, extremely weak dilutions, and
feed those to animals...but the tainted feed, and the animals with the higher rates of cancer, contained un-detectable levels of the stuff. (I've mentioned this before, but it's very easy to drive yourself insane worrying. It can be worth knowing this stuff, but please don't freak out!)
Some carcinogens aren't in people's food, but in their cigarettes. I eat a lot of carcinogens in the black pepper I use liberally at most meals, and occasionally take some with traditionally-made
root beer. I'm sure I breathe a lot in on days when I'm downwind of the freeway, or of the docks.
This labeling scheme would help some people to avoid some things, but the decision of what makes the labeling list, not to mention how it's all computed, would be extremely political. A lot of people wouldn't (or couldn't afford to) care about the labels. Even if the best science from 30 years in the future informed the labelsm, they wouldn't speak to many of the most important synthetic chemicals or to any botanical chemicals which there is no
profit motive to study, and with the CF formula set by law, it would always be out of date: based, at least partly, on studies that had later been disproven. These effects would all combine: ADM etc. would gently push stories to discredit the system, and/or lobby to make the testing regimen as expensive as possible so that their economies of scale widened the price difference between their food and that of smaller operations.
The intent is good, but I think it would be like trying to bail out a boat with a dinner fork. The tool just isn't made for the job.