Consider though that most "grass-fed" beef is grown in places like Brazil or Argentina where the native forest is cut down to make space for it. Or as an alternative consider how many cows are grown in feedlots and would instead need grassland to roam on and you can see how everyone indulging in red meat at their current level but with grass-fed beef could result in another environmental disaster.

A better way to think about this is to consider how many acres of land and how much fuel input is required to grow 2000 calories of food with an appropriate mix of macronutrients. I don't have a complete picture of what this would look like for a traditional American diet with the huge amount of meat we consume here, so I can't make an argument from that.

I do know that if we focus on acres of land and fuel inputs needed to grow protein from various sources, that plant-based proteins are much more space and fuel efficient than taking those same proteins and growing cows or chickens from them. Arguments for not eating soybeans, for example, center around how much land is being cleared to grow soybeans. But those same arguments ignore how much of those soybeans are being fed to cattle.

The best solutions in my mind are to significantly reduce our intake from meat sources regardless of how those sources were raised. Eating meat at the level we are used to is not a tenable situation.

Very few soybeans are used for cattle. The meal from soybeans is used on chickens and pigs. Cattle cannot stomach very much soy at all. They are more likely to be fed some grain, but their diet is 90+% hay and grass even on feed lot cattle. Soy meal is the leftover part of the soy bean. About 20% of a soy bean is used to produce soy oil, which is the primary source of human nutrition in soy. That's what's used to make soy milk, soy protein, etc. The meal component of the bean is not useful for all these other byproducts that soy acts as an ingredient of. So it would be a waste of perfectly good food not to feed that to chickens and pigs.

Land use management in Brazil sounds like an incredibly nuanced topic that I know next to nothing about. I'm much more familiar with American agriculture. And we make most of our own food here, including our own beef.

Source: https://ncsoy.org/media-resources/uses-of-soybeans/