The problem is that there is no evidence pampering the livestock leads to higher quality/healthier meat. Producers have an incentive to want their livestock to be healthy as is. I’d need to see some kind of evidence that US FDA standards are not sufficient based on scientific evidence. I’m unaware that there is any....I tend to doubt it as there would be a large outcry in the US a la Upton Sinclair’s “the Jungle” if livestock conditions or the conditions of slaughterhouses and processing plants were unhealthy/unsanitary.
I suppose what it comes down to is how you define ‘quality’ in meat. The criteria for quality in the UK (and Europe generally), at least from the point of view of the consumer, have prioritised flavour over appearance: whereas in the US the market appears to put more value on cosmetic considerations like size and uniformity rather than taste, relying on distinctive flavour to come from sauces etc rather than the meat itself. (I fully acknowledge this is a crude generalisation). And there’s no doubt that the flavour of meat is related to the quality of the animal’s life before slaughter.
The most tender and flavorful steak I ever had was at Jimmy’s Kitchen in Wanchai in the spring of 1969. The steak was about six ounces and I ordered it medium rare. It was cooked perfectly and I cut it with my fork. The dinner came with tossed salad, baked potato and rolls. All for $3.95. Drinks were extra.