I think there is a misunderstanding about what is meant by high welfare standards. The main purpose of standards set by the US and to a greater extent in Europe (this includes the UK) are human safety. Ensuring that the meat we eat is safe to eat. To meet those standards it is necessary that the animals are cared for in a way that does not threaten human health and so some of these standards relate to the proper care of the animals, but their main purpose is human safety, animal welfare is merely an adjunct to that.
To begin with cattle in industrial farms being fattened for market are fed corn, soy and derivatives, but cattle are ruminant animals, whose natural diet is grass based and whose digestion is not adapted to eat grain, yet all these safety and welfare standards do not ban the feeding of corn to cattle.
The BSE epidemic was the result, not of poor standards but of the introduction of animal protein, processed on hygenic, production lines that met the highest of standards, being fed to cattle, who were not adapted to eating it, while the processing freed the pathogen, that caused scrapie in sheep, but had not migrated before to other animals, to do so.
On a broader environmental basis. although figures vary, around a third of the world's arable land is growing crops, soya and corn, to feed to animals. around 70% of the world's soya crop is fed to cattle. This is wasteful way to use resources.
There are large areas of land that are only suitable for grazing cattle and poorer lands that can produce crops of hay and silage for winter feed. Cattle raised on this land is sustainable, and it could be argued, of better quality than cattle grass raised for six months then intensively fed cereals for another six months then slaughtered.
The corollary is that there will, overall, be less meat available and that meat will be more expensive. No human harm can come from this and, indeed, it can be suggested that this would be to the benefit of human health.
Two reports have come out this year saying that for the sake of the environment and, human health and survival we should move from a diet heavy in meat to one more based on fruit, vegetables and pulses. One from the UN, published by this week. The other, a French government funded, report from Science Po in Paris, you dismissed out of hand in a previous conversation we had, because the English traslation was funded by the Soil Association and hosted on its site. I am quite happy to give you a reference to the original report, written in French and not on the Soil Association site.