My question is about preventing another Civ's religion victory.
Without a religion of my own, I feel powerless to prevent another Civ from winning a religious victory. In my current game, I was late to the party for religion and didn't get a great prophet, and therefore no religion of my own. India has converted 4 civs, including mine, to Hinduism. What can really be done to stop them from converting the other 2 civs and winning a religious victory? Obviously declaring war and wiping them off the map is an option, but I'm not focused on military and they're located on the other side of the planet. I could never fund/execute a large enough war to stop them, not to mention every other civ would turn against me due to the warmonger penalty.
On a side note, why would I ever want to help spread another Civ's religion when my cities have been converted?!? I now have the option to purchase disciples with faith to further help India cruise to victory.... great. Is there really a scenario where this is useful? I suppose if the religion was a minority and you are trying to maintain a religious stalemate between 2 opposing civs this might be helpful, but seems like a waste of resources to basically be helping other civs get ahead.
Am I just totally missing something with religion here?
You aren't missing anything. Another potential solution would be to do what you can to support the religious spread (or at least religious survival) of another religion -- as long as another religion remains majority in at least one civ, India can't get a religious victory. But that's easier to describe than to execute. Of course, winning by some other method (e.g., science or culture) also works, but those require speed.