Running grass through a cow is a remarkably efficient way of converting sunlight-capturing grass into calories we can actually digest. At least in the US, much of the scrubland can't support crops without intensive irrigation and fertilizer, but they can support cattle.

If you take away the fundamental question of eating meat, it's the way cattle are raised today that's the problem.

I expect there still going to use sunlight/plants as a feed-stock in this process.