I don't currently choose my words very carefully on this issue. But after this conversation, I wonder if I shouldn't perhaps be a bit more cautious on the issue. The distinction is pretty vital. Someone can be a Catholic in good standing and hold to more liberal or more conservative views. Someone can be dead-set that priestly celibacy ought to go and still be thoroughly and completely Catholic. In contrast, someone holding to heresy is either mistaken, misguided, or evil, and should instructed, corrected, or opposed. So calling a pro-choice Catholic a "liberal Catholic" rather than a "Catholic who fights Catholicism" or "a heretic" suggests that pro-choice Catholicism is (a) a real thing, and (b) on par with pro-life Catholicism, a.k.a., Catholicism.
Nevertheless, I'm a bit concerned about switching to the more blunt terminology. My fear is pretty simple: the views held by a number of people are heretical, while the people themselves may or may not be heretics. Lots of people hold to heresies entirely out of confusion and ignorance, usually unwittingly. Someone hears "outside the Church there is no salvation," assumes that they know what it means to be "outside the Church" and goes their merry way trying to hold to what the Church believes. Someone else is raised in a liberal Catholic parish and hears that supporting the death penalty is always and everywhere sinful and takes that view as his own. I don't want to call those people heretics, because the charge is unfair. So what to do about those who agitate for views contrary to the Church's? Is there a term which captures both that what they're pushing for is fundamentally wrong, and not a matter of opinion, while still acknowledging that the people themselves may be well-intentioned and not knowingly espousing heresy?