Should you lie in order to prevent evil?

This question is generating a lot of controversy in the Christian blogosphere: the admirable Lila Rose and her Live Action team recently posed as underage prostitutes in search of abortions. Despite claiming to be underage and enslaved by a pimp, the girls were encouraged by employees of the demonic Planned Parenthood to silently have abortions. The employees refrained from reporting the pimps to proper authorities, and even explained to them how the girls could “continue working” immediately after their abortions.

Live Action’s undercover videos are now prime evidence in a national movement to strip federal funding from Planned Parenthood, so their work will probably result in thousands of babies being saved from abortion. But–and here’s the rub–to produce this good end Lila and her group lied; they intentionally deceived numerous times.

So the situation frames the question that has been debated vigorously  across the Internet: is it morally acceptable to lie in order to prevent evil, be it an abortion, a Nazi holocaust, or a terrorist attack?

Dr. Peter Kreeft, one of my heroes, says yes.
Mark Shea, another of my heroes, says no.

Though I hesitate to doubt Dr. Kreeft, I think Mark is right. And here’s an explanation why (emphasis mine):

CCC #1753 – “A good intention (for example, that of helping one’s neighbor) does not make behavior that is intrinsically disordered, such as lying and calumny, good or just. The end does not justify the means. Thus the condemnation of an innocent person cannot be justified as a legitimate means of saving the nation.

CCC #1756 – “One may not do evil so that good may result from it.”
What do you think?