That's absolute nonsense. It
is an environmental issue, and that has nothing to do with what a vegetarian or vegan enjoys eating.
It isn't about the land not used, but rather about the land that is used.
These kinds of problems don't happen when animals are pastured and pastures are rotated (not used for periods of time so the environment has a chance to recover.) No matter how you slice it, CAFOs are bad in every way other than volume of production, but especially bad for the environment. And that's something that every meat-eater who has children (or plans to) needs to understand, since this is a legacy they're leaving for future generations that is (since it is so widespread) comparable in cost to Chernobyl.
Then let's go back to that: Eliminate the CAFOs and go back to pasture-only farming. Hint: There would only be enough beef for 10% of the population who wants it, and it would be incredibly expensive.