This essay's thesis is that we should eat less meat, but its evidence is only that factory-farmed meat is a problem.

I only think factory-farmed meat is the problem. I use "eat less meat" as a shorthand, since nearly all meat is factory-farmed meat.

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The coop where I buy my meat says (pdf) that it buys only "humanely and sustainably raised" meat and poultry

I definitely agree it's better to buy "humanely raised" meat and poultry than not "humanely raised" meat/poultry. And perhaps you have found a trustworthy source.

But be careful of why I put "humanely raised" in quotes -- many such operations are not actually humane. Cage-free is much better than not cage-free, but conditions are still pretty bad. Free-range is better than not free-range, but just legally requires the animal be allowed to stay outside. There are no legal restrictions on the quality of the outside section, how long they can stay outside, or crowding. Vegan Outreach has more information.

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I might stop eating most of the factory-farmed meat that I eat. It would simply mean never eating out at non-frou-frou places. The exception would be dealing with non-local family (for local family, I could simply bring meat from the coop to share).

That sounds like an excellent idea!