When the gods made it clear that this behavior was not acceptable. I stopped. Your point about the dark void is irrelevent since the Dark Void isn't a temple and if you were able to get there, you are free to attack there. Obviously a god could still make marked spots in a city under my plan, but these spots wouldn't be inviolate. If someone can get in, they can kill you there. Furthermore, there is the added inconvenience of only other followers being able to talk to you there. So you can't just hang out in a temple and conduct business.
Another practice that is ridiculous is of first characters sitting in temples while sending second characters out to gather commodities and such. You mercinaens know who I mean. As to your post balthus: The game survived fine without this ridiculous abuse of temples for a long time. You don't need a temple to be reasonably safe if you have half a brain.