Let us suppose that Freddy the Catholic blogger is active in all forms of social media such as Facebook. If you've signed on to Facebook today you've no doubt seen a lot of those red equality signs which express support for same-sex "marriage" because the Supreme Court is hearing a case on California's Proposition 8. Freddy is heterosexual and would never commit sodomy himself. But he has some homosexual friends who seem to love their partners very much, and they seem like good people. Freddy doesn't want to be thought of as a hateful bigot so he changes his profile picture to the red equality sign. He knows that the Church disapproves of homosexual acts. In fact, he recalls from an older catechism that sodomy was classified as one of the sins that cries out to heaven for vengeance.
But Freddy disagrees with the Church about the moral status of sodomy. He knows what it is, and he knows what the Church says about it, but he writes a blog post in which he says that homosexuals should engage in sodomy to emotionally cement their relationships.
Freddy is formally cooperating with evil which is always illicit and immoral. It doesn't matter if he disagrees about the moral status of the act. If he shares the intention of those doing evil, then he is formally cooperating with evil no matter how materially insignificant his contribution to the evil might be.