Anyway, it was a data-free discussion, which is fine for what it's worth. Now comes a cattle rancher to make the same argument at Grist. To his credit he raises the methane issue, but after asking questions as to ways that, maybe, somewhat reduce methane emissions, concludes as to whether the methane is a problem, "The fact is clear. It is not the livestock; it is the way they are raised."
I may have been guilty of armwaving in my discussion with Michael, but at least I didn't jump from that to a conclusion. I left a comment saying as much, and a later commenter said it better:
It is conceivable to me that a steer that eats only grass from naturally fertilized pasture could have a negative carbon footprint. Root structures of grasses can be quite large, and soil can become a carbon sink, so the pasture could possibly sequester enough carbon to make up for the methane emitted by a steer during digestion. I'm also open to the idea that manure decomposes differently on pasture than at the feedlot. But someone needs to demonstrate it with some actual measurements and some real science.