BD, I have to disagree here with your lumping in of farmers. First, using "Civil War" stats is a total non sequitur. War is a completely unnatural condition, where disease, exposure and exhaustion are always rife. Second, while the cowboy life was undoubtedly hard on the body, farming - while hard work - is a lifestyle practiced by the majority of mankind for millennia. Out of this lifestyle has come much of our culture, our folklore, and our early technological advances. You say:
Most farmers were permanently disabled by age 40 by industrial accidents
In only a very narrow slice of time would a farmer have been subject to an "industrial" accident. In fact, I would argue that when you take democide out of the equation, more urban industrial workers would have been killed or injured on the job than farmers. They also would have lived more tragic, harder, and shorter lives. I'm reminded of Sinclair's "The Jungle" here, or even Steinbeck.
While I agree, and have repeatedly stated on this forum, that most "live off the land" fantasies are in fact just that. I suggest your presentation of farming in this thread is somewhat narrow. Yes, running a subsistence farm without modern technology is hard work, but it's far from the impossible, dismal grind suggested in this thread. In fact, most of our grandfathers or great grandfathers did it. Until fairly recently, the Amish did it. Many of us still find profound satisfaction in the aspects of our farm life that can be attended to with minimal technology of machination. Until only a few generations ago, prior to the advent of agribusiness and the proto-fascist pogrom to destroy the culture and practice of the family farm, most people did it - along with their families and communities. And many of us could do it again. Our society has largely been tamed, herded into subdivisions, trained within the confines of a fierce, intentionally designed specialization of labor. But not entirely.
You also say:
The reality is that when you go primitive, your chances of dying of disease and accidents is going to be very high
"Very" is a relative term. When one goes urban, their chances of contracting diseases is also quite high, also as a function of their environment. Consider the modern rise of diabetes and various diet-related cancers, stress disorders, and mental illness. Not to mention auto accidents and crime statistics. When we compare within the same time periods, urban workers were subject to the same if not higher rates of disease and acciden, and certainly more at risk for infectious diseases such as small pox than their more isolated rural cousins. Also remember that those lifespan stats are heavily skewed by early child mortality.
Finally, of we consider a "collapse" (to use the thread's language), those in urban and suburban clusters are going to be at far more immediate risk of disease due simply to population density and dependence on common services for water, heat, electricity, etc, not to mention an inability to produce food.
Farming, without modern technology, is certainly not for everyone. But it's hardly the short, brutal life made out in your post.