Mark Shea apparently opened the discussion with a post whose closing I will quote to give a good sense of the tone.
The trick that Catholics influenced by libertarian ideology (aka heresy) need to master is this: instead of ransacking Catholic teaching for the subsidiarity bits that happen to comport with libertarian heresy, instead embrace the fullness of Catholic teaching, including the Church’s teaching on solidarity, the common good, and the legitimate role of the state.
Joe Hargrave replied in Crisis. Here's his closing, for comparison:
All of this is to say that complex economic and ethical issues cannot be resolved by shouting “heresy!” It would be antithetical to the spirit of Catholicism to suggest that anything other than the common good ought to be the ultimate goal of economic policies. It would also be antithetical to the spirit of Catholicism to suggest that there is only one way to promote it, and that all other ways are automatically heretical and forbidden. Libertarianism is only a “heresy” in the same way that every other idea becomes a heresy; when it is taken to irrational extremes or when it explicitly rejects a fundamental teaching of the Church. There is no reason why any self-identified libertarian has to do either.
Shea then took to Facebook to respond and basically repeated himself:
I recognize that there is no libertarian magisterium and that people pick and choose bits that they like--and that lots of people influenced by libertarianism are very nice people and very good Catholics. I also recognize that all they are doing is selecting bits and pieces from Catholic Magisterial teaching and that the more Catholic you become the less Libertarian, while the more Libertarian you become, the more like Murray Rothbard you become. My solution: ditch Libertarian heresy and just stick with the fullness of Catholic teaching.
Shea clearly comes off as the one taking the low road here, while Hargrave writes a reasonable post and wisely resists the urge to follow Shea into accusing everyone he doesn't agree with of being a heretic. Shea's writing has been heading down hill for a long time, but I was nonetheless surprised by the contrast here.