The UK has very strict requirements around certain foods that their farmers have to meet. Allowing US farmers to bypass those requirements will undercut those domestic farmers and while individual consumers may still opt for the more expensive domestic option, restaurants and takeout businesses will usually opt for the cheapest option which introduces it to the country even if the consumers don't want it. It's not like McDonalds has a sign that says "Made with US Chicken!" on your nuggets. Secondly, allowing cheap US chicken just penalizes the poorest in your country that will go for the cheapest option to survive. Some people don't have choice and food standards help bring the bottom up.

While we’re at it, why not let manufacturers reintroduce lead into paint and toys and let consumers choose what they want there too? The problem is that “consumer choice” is frequently a shield for amoral companies to take advantage of information asymmetry to externalize problems onto individuals. Individual consumers do not have time to deeply research every purchase they make and so it is not reasonable to expect them to handle these things themselves. Instead we have the Hobbesian contract where it is much more efficient to empower a government to centralize the handling of these common goals. It’s not smart or edgy to argue for the “free hand of the market” in these one-off topics, because none of these decisions are made in a vacuum but rather are part of a continuum of choices that the governed are mostly happy with (no such safety regime can ever be perfect).

Because we know the implications of poor quality food, and we also know those who would buy it have no choice but to buy the cheapest. So, no thanks. I'd much rather the state intervene here and keep this crap out. This "let consumers choose" argument is tiring when consumers don't have the ability to choose. They are just trying to survive

We have decided, we elected a government and had it pass food safety laws.

They kinda did using that representative democracy gizmo

Why enable a race to the bottom? They don't take our dubious food colorings, either.

Why would a citizen want their representatives to allow bad meat into the country? What would their thought process be here?

Chlorinated chicken has become a big talking point in the UK and there is overwhelming public support for continued ban.

because the US always insists on changing labeling rules so consumers can't

even if this wasn't the case, the substandard US product will end up replacing UK product in everything that isn't labelled (processed foods)