Why should one consider that morality may be objective?
In our favorite sins, we tend to cease being objective. We have difficulty seeing why they are bad if they obtain a good for us whether pleasure, wealth, power, and/or honor. Is it not convenient that we would conclude that there is no objective morality at all, especially concerning those sins to which we are habituated? Perhaps to one of us, rape is good and to another, it is the only unforgivable crime. However, the question is not so much whether a good is attained it is whether there is a good that ought to be there. In the case of rape, firstly consent, secondly someone who really loves you, and thirdly the proper use of the sexual faculties. Objective science supports not only the happiness of the religious life but also the proper use of sexuality. Only studies that are slanted in their assumptions support the frequent and unbridled use of sexuality to obtain happiness. Since this is a key issue for society, here is a more in-depth look at this:
Happiness from Virtue or Indulgence? (click picture to Read)
Other areas of morality
Even if we digress from the sexual sins, we will find there are at least social norms that also correspond to the general well-being of the community and individuals. No society, for example, that allows or encourages child abuse of any kind can be said to flourish since itis by nature self-destructive. Whatever one may subjectively feel about morality, the metric the Church uses for understanding what is/is not moral is the concept of harmony. Does an action or set of actions bring detriment of any kind or is it all good in its intention, context, and method? If it is all good, it is moral. If there is an aspect that may be corrupt, then it either ought to be not done (in the case it utilizes evil means such as killing someone), or the necessary good should be supplied ensuring it is made good. Love is willing the good and this is what man is made for, says the Church/Christ, that which is objectively to it (the good or willing it) contrary is objectively immoral.
Conclusion
There are many studies that support the Catholic moral understanding for one aspect or another, concurrently there is a lot of misinformation that is popularized concerning such things, especially sexuality. The Catholic ideal for morality has not been tried and found insufficient but rather found difficult and never tried. Justice finds all. Love, however, is what Christianity brings to the world not just in feelings but in its fullness.
Catholic Moral Theology often takes into consideration psychology and medical science which is consistent with experience and other/corresponding truths of science when developing a moral understanding of new moral situations. The Moral teaching of the Church is available in the Third Part of the Catechism, it is worth noting one should not start their faith journey only by moral adjustment, even if some aspect can be helpful. It is from the Church's understanding of what man is and what he is for as revealed by God, which is beautiful that the conclusions about what is and is not good for him are formed. One should begin there first, understanding the premises, rather than confronting the conclusions without them. Nevertheless, the Church would claim that morality is something that can be known apart from the feelings guarding supposed convenience, just as the ancient philosophers did. Making our own "god of the state" (in place of God's laws), communism becomes the only moral framework where a fair equilibrium is actually established and maximized such that if anyone is poor all are. The truth here is that it does actually attain that end because humans are corruptible creatures.
Now that you have been introduced to the Catholic understanding of how morality is involved in faith and how it is very helpful to man to believe in the Christian God in particular morally, let us consider materialism.