The issue is with alcohol and cigarettes, people do have the choice but we restrict it to over a certain age (and tax heavily for doing it).
The issue with food is less the individual making the choice, it’s them making it on behalf of their children. My wife works in a primary school and the amount of kids that only get a decent meal at school really is depressing.
Not a brexit thing as such, but to me we should never be looking to reduce standards or regulations around awareness of food content.
There's the knock on effects for the health service as well. Lower food standards will mean lower cost to the consumer at the til, but we're already a pretty unhealthy nation as it is, and this could contribute further to the burden on the NHS in the long term. It seems tho that the reason we won't introduce legislation on this is that it would knacker any deal with the USA.