Eh. I mean, I think we may disagree about what constitutes "subsistence farming". Or if we don't, instead, I'll submit that subsistence farming looks very different in a developed country than in a developing country.
I mean, what drove urbanization in the the 19th century (in the US, Europe and the Middle East, and likely elsewhere)? Here are two important factors: advances in medicine and agricultural technology.
First, before that point in history, farming households had as many children as they could as a hedge against the deaths of their several of their children to illnesses that were easily preventable with the rise of modern medicine.
Second, advances in agricultural technology that arose in the course of the latter half of the 19th century enabled 10x or even 100x efficiency, and gave those who had those technologies a decisive competitive advantage against those who didn't.
Together, those two factors meant that rural communities had larger populations than they could sustain: because modern medicine was readily available, children didn't die of preventable illnesses, and because of efficiencies in agriculture due to technology, there were fewer jobs available. There was, in other words, a surplus of labor in rural communities, at the precise moment when there was a rising demand for labor in cities due to industrialization. Hence, urbanization.
What am I getting at? Not that capitalism undermines ways of life based on subsistence farming, which of course is something that I just described. In other words, something close to what you were getting at when you said this:
I'll add, I don't feel like that's a point I need to concede, because I don't think it undermines my position. I'm not arguing that capitalism is some kind of moral force in the world.
No: what I'm getting at is that subsistence farming in the middle of the 20th century, when it was still possible to take advantage of modern technology and modern medicine, looks very different from subsistence farming when you can't. Many people in the developing world who practice subsistence farming are not practicing that type of subsistence farming. Their form of life is fundamentally unchanged from how people lived 500 or 1500 years ago, and just as arduous.
Of course. What's remarkable is that people in developing countries still choose to move to cities to have a chance at a better life, if not for themselves, for their children, and to escape what are effectively pre-modern conditions of life, despite the fact that it's absolute hell (just as it was for those in the 19th century who made similar decisions).