Seriously, though, bromate, when fed to mice in massive quantities, causes cancer. Mice. Massive quantities.
So what ;-) That is true of all carcinogenicity studies. Dosing in massive quantities over a lifetime in species other than humans. And 98% of the chemicals that are classified as carcinogen are classified because of the results of such tests. So if bromate causes cancer in mice when fed massive quantities over a lifetime, that would be reason enough to classify bromate as a carcinogen. But wait, there's more.
There has never been (nor will there ever be), a correlation between bromated flour and cancer in humans.
That is because bromate in flour does not lead to exposure to bromate from baked products. Bromate oxidizes flour components after addition of water (making dough) and heat (baking), and gets converted (quantitatively) into bromide. So any risk assessment of bromate in flour will result in zero exposure, and, as such, zero risk, no matter what the hazard of bromate is.
Now whether you want to base yourself on the outcome of the actual risk assessment or want to regulate based on hazard (read: chemophobia), depends primarily on your political outlook. The US chose to be pragmatic, whereas the EU chose to follow the chemophobia path...