And a second is "how much better or worse is this animals life compared to a similar animal in the wild?"
My personal opinion is anything that doesn't meet the first benchmark is evil. Anything that is between the too is in a gray area. And anything past the second I don't need to feel too concerned about, or I'd describe it as ethical husbandry.
It's clear that there are plenty of chickens whose lives are soo terrible that don't meet the first benchmark and their extinction would be preferable to their current experience
The second is also easy. Nearly every animal that is farmed has a much better life as livestock than as a wild animal. Want your last day to be a bolt through the brain after getting to gorge on food for weeks, or chased down and your guts ripped out and eaten while you're pinned down in terror?
If you were a non-human animal, which life would you prefer?
And yes, pig and chicken operations like that should be stopped.
Why is that, though? I would reckon that most animals on the Serengeti (not Bison, mind you) live out their average lifespan. Sure, some percentage of them are eaten or die to drought, but there is a reason that their average lifespan is 15--20 years, or whatever it happens to be. Compare that with the 5--6 year average lifespan of a factory farmed animal. It is hard to give you a more detailed argument without understanding the real reasons behind your value judgement.
I don't think we'll be able to move beyond subjectivity for the morality of this, but I do think we can be more precise.
A cow, a goat, chickens, sheep, whatever you want, managed by the family, free range, decent life before being slaughtered.
That seems like it would fit those benchmarks quite well.
It's how it was done in the past, people were self-sufficient when it came to food. Big agriculture companies could provide food for the people and these animals, so they would still exist and be profitable.
The problem is that land is limited, and spreading out would just result in extremely inefficient fuel usage, with all the pollution that entails.
Plus, some would say it would be a pretty inefficient use of man hours, although I think it would be a better, more "natural" life for humans, as well.
Everything I've read or heard says there was quite a bit of malnutrition and hunger.
I know people who have chickens, ducks and vegetable gardens and work full time - indeed, only possible because they simply buy animal feed and have an automatic irrigation system.
It's still and extra hour of work a day, though, not counting harvest and slaughter time.
Of course, that's nowhere near enough to cover their needs.
But in this context, simply getting rid of the garden and having just an animal farm, while buying everything else from big farms makes a lot of sense.
You still get enough food, you still eat eggs and meat, and the animals live happier, longer lives.
I do think it's important to understand that humans are animals, and that they are not uniquely immoral within the animal kingdom, but the fact that something happens in nature isn't sufficient in order to morally justify it. Humans ARE unique in their capability to reflect on the morality of behavior at a high level.
Where I think your argument is strongest, as I said, is in response to the claims that humans are uniquely malevolent, as if most species aren't constantly maximizing their acquisition of resources within the boundaries of their capabilities. That just doesn't mean that we have carte blanche on all behavior we can observe in nature.
You clearly have no clue as to the intelligence of these animals and the complexity of their desires beyond being "pampered, fed, and protected". If it were you, would you rather take a chance on surviving in the wild? Or being enslaved, separated from your children, shackled, fattened, and eventually butchered is preferable?
There is no good measure tape available.
There's a difference between having moral worth and being a moral agent. Non-human animals (generally) cannot contemplate the ethical character of their actions, so they are not moral agents, nor should we consider them such. This does not mean they are unworthy of moral consideration. What is being evaluated is the ethics of the behavior of people who are moral agents, and there have been guide sticks for the behavior of people for as long as people have been thinking about ethics.
However, I think saying that there is "no good measure tape available" might be intellectually dishonest since we can probably come up with a rough model to optimize for the minimization of global suffering of all beings involved.
Obviously, most mental models have a higher weight biased for humans rather than animals, so a suffering factor for humans would have a higher multiple than for animals. That is where most of the controversy seems to be.
Possibly a wolf, Siberian tiger or large brown bear would predate a cow, similiar to the predators of a moose but it doesn't seem like they are under constant fear of predators any more. Cows are often left to pasture across vast unfenced area of basically wilderness and don't seem particularly afraid nor at risk of predation (otherwise they'd need to be guarded).
For a consistent framework of ethics, these animals should be treated essentially as lobotomized humans.