I would suppose to prove his theory he can show in countries with high Catholic populations there is a high rate of AIDS...
Using the facts provided by the CIA Factbook and Nationmaster.com there certainly is some correlation between Catholicism and AIDS rates, for example the following are countries followed by % of population with AIDS and Religious content:
US - 0.6% - RC 24% Prot 52%
UK - 0.2% - RC 8% Prot 63%
France - 0.4% - RC 88% Prot 2%
Italy - 0.5% - RC 95% Prot <1%
Spain - 0.7% - RC 94% <1%
Australia - 0.1% - RC 26.4% Prot 41%
China - 0.1% - 95% Daoist (Officially Atheist)
I have included only reasonably wealthy countries to ensure that each has a decent system of education and access to condoms. Most of the third world catholic countries support the above theory even more strongly, but are an unfair comparison due to low levels of education and poor condom availability. Now clearly there are many other factors affecting AIDS infection rates, but even with some exceptions there is a certainty of around 80% that a country with 25% or above Catholic population is will have more AIDS sufferers than a country with less than 25% Catholics.
It may be that lower condom use in catholic countries leads to higher AIDS populations, but I somehow doubt it. If someone was sufficiently strong in their belief not to use condoms, then one could safely presume that they would also be sufficiently devout to not practice sex outside marriage, thus with only one partner infection could not occur. Or am I being naive? I know many single catholics indulge in sex outside marriage, but do they use condoms or not? Would a single catholic feel better about himself having sex with a condom than without? Is unmarried sex without a condom less of a sin then unmarried sex with a condom?
The correlation between catholic population and AIDS percentage is clear, but the reasons why, certainly are not.