Unlike protestant faiths which creates new members through active evangelism, all of the 1 billion Catholics creates new members through procreation & child baptism. The number of evangelical movements in the catholic faith is very low compared to protestant faiths.
Since their gods are not omnipotent enough to pay bills, all religions need new members for their monetary needs (i.e. paying clergy, maintaining religious facilities like buildings & churches). So the catholic faith cannot afford to have a lesser birth rate in their religion.
This is why the pope is very scientific when it comes to evolution & big bang, but very unscientific when it comes to proven methods for disease prevention. Therefore he cannot allow condoms in his religion.
It could be possible that soon all protestant faiths might unanimously ban condoms too. That will happen when, their membership count is large enough to be sustained through procreation alone and with very little evangelism.
We atheists must focus on de-converting the evangelists because, nobody is going to stick to the no-contraception rule. So if we persist for, say the next hundred years on the evangelists, we can cure enough people from this virus of the mind, and perhaps even prevent their self-fulfilling eschatology from happening.
(How do I know this: All of my ancestors have been catholic for a thousand years. I was catholic too, until recently.)