That's not to say you are wrong about them in particular, but our particular ecosystem it's different. However, the grazing on public land isn't all good. In chokepoints sometimes land destruction happens, for example.
That being said, the idea of leaving pristine wilderness that way for the sake of it fails the understand the bigger picture I am talking about here. For example, if we were to leave the pristine wilderness to do it's thing, we should let natural burns just do their thing. That's part of my original statement. The forest service was interfering with the natural process of burns in the forest and in the end caused more damage than benefit.
The livestock have helped keep underbrush down, and since the fires have helped to spread plant life and reinvograte the forest. The ranchers in tending the stock have also performed many of the duties that the forest service otherwise would do, and often don't have the time, manpower, or funding to get done. Honestly though I just happen to be a geek from the area, I don't know that much about the grazing system and I would have to ask the people who do know about it.
So to summarize, my list of good things are: reduced wildfire risk, increased plant diversity, invasive plant control, and reduction of public funds needed for land management (I've seen estimates at over $750m saved per year by public grazing programs nationally).
I have to say a response like yours is exactly what I'm talking about. The kind of knee-jerk "save the land" response without considering the pragmatic reality of the situation. Ranchers alone, if done properly, could keep the pristine wilderness more pristine than if it was all just walled off and no-one ever went there.