The grass most cows eat also need to be planted. The point of this post is that we could be planting stuff we can eat so you don't have to 'pay' the conversion cost.

That depends entirely on where you are.

In India, for instance, dairy cattle are fed almost exclusively on crop residues and by-products. Crop residues being what's left over in the field after you harvest and by-products being what would otherwise be waste left over after you process for human use.

Elsewhere, in addition to crop residues/by-products, you also have natural grasslands that aren't planted or irrigated, legume feed grown between major crop seasons when you can't grow anything else that also replenishes the soil and feed grown on otherwise marginal land or barely managed land.

Certainly some crops grown for cows would be edible by humans or the land repurposed for growing crops edible for people, but there's often a cost involved like heavier fertilizer requirements, pesticide use, water requirements, added infrastructure and/or labor.

The grass cattle can eat (which doesn't need to be planted; most people around me don't regularly plant their pasture) is not stuff people can eat, and can often grow in conditions that can't grow people-food.

Specifically, they can eat stuff that doesn't require constant fertiliser inputs, where as people-food generally does need a lot of fertiliser inputs and needs more intensive herbicide/pesticide application.

A balanced approach is to go, "Hmm, it's probably a good idea to raise cattle, chickens, and other animals, and also to grow all kinds of produce and staple crops as well."

No, not all land isn’t the same. It is far more profitable to grow a high value crop vs plain grass. But some land just isn’t great for other things than grass. You have large cattle farms in Australia where you can’t grow anything other than grass and other wild plants.