In Chapter 14 of Guns, Germs, and Steel, Jared Diamond discusses the ways in which religion serves to prop up and legitimize kleptocracies. Kleptocracies are governments that take wealth from the relatively poor masses and transfer it to the relatively rich elites. Essentially all governments in the modern world are, in Diamond’s view, kleptocracies. If a Catholic believes Diamond’s argument, it becomes harder to try to propagate the faith.
It is easiest for a Catholic to try to maintain and spread the faith if he or she believes that the faith is a good thing to believe in. If one accepts Diamond’s argument, this is hard to believe. If you believe Diamond’s argument, then you believe that religion works mainly to make people believe that it is right for their government to act as a kleptocracy. Diamond also says that religion works to make people more willing to die for their country. It would be much harder for a Catholic to enthusiastically spread the faith if he or she believed that, by doing so, they were simply making it easier for kleptocratic governments to get their way.
This is how Diamond’s view of religion (if we accept it) makes the mission difficult for Catholics. It makes it harder for them to believe that it is unambiguously good to spread the faith because they might come to think that they are actually encouraging people to blindly follow a kleptocracy.