One of the rally’s keynote speakers stated the erroneous opinion that the greatest evil facing us today is abortion. But according to St. Thomas Aquinas “[t]he sin of unbelief is greater than any sin which occurs in the perversion of morals.”  The sin of unbelief is therefore greater than murder even murder of the unborn through abortion. This is not to minimize the evil committed in abortion but to clarify that not all sins are equally grave and that abortion is not the gravest of sins. St. Thomas reasons that “[t]he gravity of sin is determined by the interval which it places between man and God; now sin against faith, divides man from God as far as possible, since it deprives him of the true knowledge of God; it therefore follows that sin against faith is the greatest of all sins.”  There are many ways a man may sin against faith  and one way of doing so is by heresy. Heresy is a type “of unbelief, belonging to those who profess the Christian faith, but corrupt its dogmas.”  Thus Protestantism and all those other non-Catholic religions that claim to take the title of “Christian” are heresies for they reject some, if not many, of the dogmas of the Catholic faith.
And who can deny that heresy is not in existence in America today? There are tens of thousands of different non-Catholic “Christian” denominations operating in our country, each claiming to be following Christ and yet each rejecting at least one or more dogmas of the Christian faith. Furthermore, and with greater concern is the fact that many professed Catholics reject some of these same doctrines. Polls show that the great majority of self-proclaimed American “Catholics” dissent from the Church’s dogmatic teachings on abortion, contraception, divorce and remarriage, and on the Real Presence of Christ in the Holy Eucharist.  And in Latin America Protestantism and secularism have made significant advances in once solidly Catholic countries. According to a new study the Catholic population in Brazil is shrinking more rapidly than ever and that “the Catholic share of the population [in Brazil] hit its lowest level since census figures tracked religion beginning in 1872, bottoming out at 68 percent last year.” 
So abortion is the greatest evil? Think again.
 Summa Theologica II-II, Q. x, a. 3.
 Atheism is one example.
 Summa Theologica II-II, Q. xi, a. 1.
 See, e.g. “A Gallup Survey of Catholics Regarding Holy Communion,” January 1992.
 “Brazil’s Roman Catholics shrink as secular rise,” Yahoo! News, October 8, 2011; online text available at: http://news.yahoo.com/brazils-roman-catholics-shrink-secular-rise-071216935.html.