Not sure a pig farmer has the best perspective on this. I've been on farms in my area, that have land that is not usable for farming, too many rocks, too hilly, etc. The land has enough natural rain-fall and grasses that grow on it to sustain sheep/cattle where there would otherwise be nothing but a fire hazard come the dry season (California).

In this one and perhaps not common scenario, I think eating meat from these sources, slaughtered humanely, is reasonable. This obviously is not enough meat even for locals in my area to be having burgers daily, so a huge reduction in meat consumption is needed even if one wants to continue eating meat 'responsibly'.

This article unfortunately does not mention that grass-fed meat has different omega-3/omega-6 ratios than factory farmed, and eating smaller quantities of grass-fed meat is healthier than larger quantities of factory farmed. Not sure any meat industry person, even sustainable, is going to mention that cutting back from typical American consumption is a good thing.