Perhaps one day we will let those areas re-grow without interference again, but until we're past the expected peak of 12 billion people on this planet about 100 years from now, we're going to need every calorie we can get hold of to prevent mass starvation, considering we're also going straight into a top-soil crisis, depleting groundwater reserves by massive irrigation, and so forth.

But yeah, I was mainly referring to natural grasslands where the original grazers have been replaced by grazing cattle. De-forested land should be re-forested if it can't be used for anything else.