I realize that none of the commenters here are Catholic progs, so that they suffer not from the disease he addresses. I doubt any such progs even read this blog, since they know by now that they will rarely if ever hear anything they really want to hear. But I believe May's article supplies non-Catholic Christians with a much-needed overview of what sorts of assent are required of Catholics and hence what sorts of dissent are permissible or impermissible for them.
That is important for my vast readership because, I have found, one of the most common complaints about the Catholic Church from Orthodox and conservative Protestants is that she is not tough enough in practice on dissenting Catholics. Leaving aside the irony that what's being complained about is the freedom of some Catholics to reject with impunity beliefs that the complainers also reject, I happen to share the complaint. But the problem is not one of theory or even theology; indeed, the fact being complained about is no evidence that what the Church teaches is untrue. Rather, and in some cases, it is evidence that bishops with the responsibility to deal with public dissent fail in their pastoral duty. But I also don't quite get what further conclusion is supposed to be drawn from that. Since there have been negligent and even heretical bishops ever since there have been bishops, it should hardly shock that such bishops exist in the Catholic Church today, when she is concerned not to revive fears of the old Inquisition—an institution for which, of course, she is still taken to task regularly enough.
Like Chesterton, I find it to be one of the marks of truth in Catholicism that it is so often subject to mutually incompatible criticisms from opposite sides of the spectrum of her opponents. We see the same phenonomenon in intra-Catholic disputes too. To the trads, Rome is too liberal; to the progs, Rome is too conservative; and both believe that some Catholic teaching today is discontinuous, even incompatible, with definitive teaching of the past. As I've explained before, I'm a "neoCath" because I find in the hermeneutic of continuity the only way to be both an orthodox and an intellectually honest Catholic. I hope that May's article helps others, especially Catholics, to get there if they aren't already.