The article title is misleading.
He's criticizing the
way livestock is produced.
There is a trend to replace industrial agriculture with organic agriculture. The latter can actually yield
more crops and livestock and is better for the environment.
The production level remains the same or more. The eating level remains the same more. The amount you poop out remains the same or more.
The only one actually claiming that Americans need to eat less is the author of that article. He quoted a UN statistic. Charles didn't actually say that in his speech..
"Americans eat more than 41kg of beef a year on average, according to the UN, almost twice that consumed by Britons and four times the international average. "
Here's a link to the article:
Prince Charles tells America to cut down on steaks ... for the sake of the world - Telegraph