There is zero scientific evidence that either chlorine or other chemical washes they dunk the chicken breasts in in order to kill the bacteria on them is harmful to human health. None. Zero. So they can't claim its "unhealthy".
No, their complaint is that it works too well. Its too effective....meaning you could have dirtier chicken houses yet still produce perfectly safe chicken because this process is so effective at killing germs and bacteria. So based on nothing more than the suspicion that health standards in the poultry industry are lower in the US but can be compensated for by a chlorine wash of the chicken meat, the EU and UK have banned it.
In the same way that gosh, they'll just have to ban those American high tech companies for allowing free speech on their platforms. EVEN INCLUDING US Citizen Musk interviewing US candidate Donald Trump in America for a US election on his own platform. YES! They actually said/did this!
Personally I think we ought to say American roads are allergic to European cars and therefore we can't have any cars produced in Europe on our roads. Hey, its just as reasonable.
Football helmets are the cause of all manner of head injuries if you ask a rugby player. You get shoulder injuries in rugby - CTE not so much.
Safety standards are often a cornerstone for an industry maintaining a regulatory competitive advantage. So can you even sell chicken without a chemical wash? IDK. If so, that woul be a nice way to stop me from buying from the Ahmish down the street.
Same deal with US requiring all milk be pasteurized - you can have horrible cow hygiene an get away with it - except for horrible tasting cheese that has lost all manner of nutrition and beneficial bacteria.