I've written before about the reluctance to ask the question, "But is it true?" Often this reluctance is due to doubts of the existence, knowability, or value of the truth.
Sometimes, though, it's due to a preference for what seems like a stronger argument than, "This is true." Among Catholics, the stronger argument is often, "This is what the Church teaches."
Obviously, if what the Church teaches is true, then a demonstration that the Church teaches something is implicitly a demonstration that it is true. As obviously, though, what is true is not necessarily taught by the Church.
There are two tricks to using a "The Church teaches it, so it is true" type argument. First, recognize it is an ad hominem argument, in the sense that it only works on people who believe that what the Church teaches is true. Second, make sure the Church actually teaches it.
The two tricks are related, since the manner in which "the Church teaches" something determines the willingness of people to accept that it must therefore be true. Some Roman Catholics feel free to doubt anything outside the Nicean Creed; some Roman Catholics accept as dogmatic every speech given by this Pope (but perhaps not by that pope).
There are several claims against the university and everyone involved. The weakest claim is that using these cells is imprudent and potentially scandalous. A stronger claim is that using them is immoral per se. The strongest claim is that using them is contrary to explicit Catholic doctrine.
The first claim can be true without the others being true. The second claim can be true without the third being true. This matters because, as far as I can tell, the third claim is not true.
By their very nature, matters of "mediate material cooperation in evil" -- an act in which the cooperator has a different moral object than the evil with which he is cooperating and which is not required for the evil to occur -- resist being settled doctrinally. Statements by theologians, Curial bodies, and even the Pope serve as evidence for a particular viewpoint, but they do not constitute the explicit Catholic doctrine some people appeal to as a means of anathematizing those they disagree with.
As with Peace and Justice Catholics, I urge pro-life rigorists to carefully distinguish between actual Church doctrine and prudential policies derived from doctrine. Others are not necessarily less Catholic than you simply because they do not agree with your prudential policies.
In other words, a petition to a bishop along the lines of, "You do know how evil you're being, don't you?," is unlikely to help.