When Is A Lie Not A Lie?

Here's Robbie George wondering if those LiveAction videos exposing Planned Parenthood are actually moral. I'm not caught up on the whole conversation yet, so won't comment, but basically the matter comes down to an old debate:
The question in dispute between them is whether lying is a legitimate means.  Tollefsen, in line with the teaching of St. Augustine, St. Thomas Aquinas, and the Catechism of the Catholic Church, argues that lying is always and everywhere wrong, and may never be resorted to, even as a means of preventing wrongful killing and other grave injustices.  His account of the moral wrongness of lying focuses on its damage to the integrity of the liar and to the relationship (the communio) of the liar and the person to whom the lie is directed---damage that is unavoidably done whether one's lying is in a good cause or a bad one.  Kaczor appeals to a counter tradition, one associated with Cassian and St. John Chrysostom, that maintains that there are narrow circumstances in which lying (to those who have "no right to be told the truth") is permissible as a means of frustrating the efforts of a grave wrongdoer to achieve his evil objectives.
George seems to think the Catechism has settled the matter in favor of the former position. I'm thinking about it.
I raise it, however, because my anti-Kant rant last week touched on a similar point, and one of my commenters thought I took the matter of lying to Nazis too lightly (which I admit I did, but my point was about the finiteness of the human condition). Anyway, a commenter at the link shares my own initial reaction:
I can't help but note the comparison to the all-encompassing torture debate of recent years. There was an enormous amount of righteous indignation directed against the idea that one could legitimately debate the scope and meaning of "torture" and acknowledge the hard cases. I'm not sure there's any difference in our present case: "lying" is one of those words where "everyone knows what it means," and yet people are far more willing to debate its scope and meaning and acknowledge its hard cases. The blood just doesn't boil as much and as a result, real inquiry into something we don't know as well as we think we do is possible.
That was my criticism of certain popularizers of Catholic teaching:  the tendency to turn "discussion" into no discussion at all. I would have liked to have had the actual argument rather than just be boxed about the ears.

Update: Various: It is a sin to lie, even to Planned Parenthood. Dawn Eden's post Building a culture of lie; Mark Shea unsure. And then surer. And Pat Archbold on Just Deception Theory.