If....a heretic and a man trusting heretics seemed to me one and the same, I should judge it my duty to remain silent both in tongue and pen in this matter. But now, whereas there is a very great difference between these two: forasmuch as he, in my opinion, is an heretic, who, for the sake of some temporal advantage, and chiefly for the sake of his own glory and pre-eminence, either gives birth to, or follows, false and new opinions; but he, who trusts men of this kind, is a man deceived by a certain imagination of truth and piety.
It is safe to say that nowadays, and perhaps even back then, the majority of Catholics "trust" heretics, and pretty much for the reason Augustine gives: not because they recognize them to be heretics, but because they are "deceived." Hosts of ordinary Catholics uncritically glean opinions from people such as Marianne Williamson, Deepak Chopra, Dan Brown, Elaine Pagels, and even Joseph Girzone, to name just a few. With the possible exception of Brown, those people are plausible and, in their own several ways, attractive. Girzone is a retired priest whose novels give us a Jesus many of us prefer; that Jesus is plausible because he's enough like the One and Only to be reassuring but not so much as to be threatening. I've even seen Williamson up close: she's a knockout; as a healthy male, I want to believe her even when I can't. I understand the appeal of such people, most of whom have made a fortune peddling their ideas. But that's rather the point. To borrow a phrase from Rupert Murdoch, an unabashed man of the world whom I admire as such, what it's basically all about is "giving the people what they want." There's a huge market for this stuff, and many Catholics prefer it to what they get, or perceive they get, at church.
The problem thereby posed is that most Catholics, whether adolescent or adult, are hard to educate and form as Catholics. Ideas fundamentally incompatible with the authority of the Church, or with the content of what's proposed by such authority, are packaged and marketed much more appealingly than the truth and are aborbed almost by osmosis from the hyperactive media culture. Accordingly, a great many Catholics don't even understand what you're talking about when you talk about the Magisterium, orthodoxy, the Hypostatic Union, and so on almost ad infinitum. For them, all that sort of thing is an historical curiosity at best, an interesting academic exercise that might be worth taking seriously only if the clergy actually made a point of it. (Dorothy Sayers had some entertaining, and quite pointed, observations on this in Creed or Chaos?) This is why it's no good condemning such people as heretics. They don't know enough of the truth to be accounted morally culpable for rejecting it. And that, I suspect, is the reason so many clergy rationalize their failure to present the whole truth and challenge Catholics with it. They fear raising people to a level of knowledge that might actually render them morally culpable for rejecting what is irreformably taught by the Church. And so, hordes keep marching right up to communion without even believing—never mind living—even half of what the Church has thus taught.
Then there are people whom it is hard to believe are inculpable. I mean the aging, intellectual heretics who sort of stay in the Church and retain a strong following among their generation of Catholics: Hans Küng, Joan Chittister, Charles Curran, Rosemary Reuther, even Luke Timothy Johnson, to name just a few. The energy of such people and their followers is the passion with which they reject what was, in their youth, the recent past; they still speak with the voice of a Zeitgeist slightly beyond its sell-by date; yet the residual appeal and confidence stem from the sophistication, which masks the sophistry, of their arguments. Consequently, many Catholics in their 50s, 60s, and 70s trust such people far more than Rome; as Fr. Neuhaus says, dissent "is the tradition of which they are the traditionalists." Much of the difficulty even today in forming Catholics arises from the fact that many of the personnel who are, or would be, formators were formed by such intellectual leadership. Of course we needn't worry about that too much and too long. Young people are not inspired by "progressive" Catholicism, which by and large has become sterile and cynical. Progs certainly produce fewer babies and priests than their intellectual peers among the orthodox.
And so I don't think the problem is what to do with the real heretics. Both individually and demographically, they excommunicate themselves. The problem is what to do with the people who, remaining faithful to the Church by their best lights, trust heretics they are too ignorant to recognize as such. Telling such people they're ignorant won't win their ears; the only solution is to present the full, undiluted truth in ways that actually engage what most people hear and are subtly sold.
I hope you're game for that. I am, whether or not I get to earn a living at it. But I think I'd be more believable if I did!