I'm not staunchly defending the beef industry or factory farming for that matter, but I believe much of the land used for cattle grazing out west is not arable land suitable for much else. At least not without a corresponding change in agricultural habits, like massive irrigation that further impact a stressed water resource.
https://news.cornell.edu/stories/1997/08/us-could-feed-800-m...
https://en.wikipedia.org/wiki/Digestible_Indispensable_Amino...
Beans are great, but the amino acid ratios aren't ideal for humans and they are deficient in certain essential amino acids which we can't synthesize. It's certainly possible to get near optimal ratios and quantities with a mix of plants but this takes a bit of planning.
This is true for any processed food. And I’m using “processed” liberally here. Meat must generally be butchered, and salted/smoked/cooked before consuming, but we’re just so used to it we don’t consider it “processing” or “planning” to do it.
https://www.weforum.org/agenda/2021/02/7-commodities-forests...
>Most of the UK and Ireland’s grass-fed cows and sheep are on land that might otherwise be temperate rainforest – arable crops tend to prefer drier conditions. However, even if there were no livestock grazing in the rainforest zone – and these areas were threatened by other crops instead – livestock would still pose an indirect threat due to their huge land footprint
(and those "grass-fed" cattle are also fed crops too)
>Furthermore, most British grass-fed cows are still fed crops on top of their staple grass
https://theconversation.com/livestock-grazing-is-preventing-...
>If beef consumption is not reduced and is instead satisfied by greater imports of grass-fed beef, a switch to purely grass-fed systems would likely result in higher environmental costs, including higher overall methane emissions.