Removing a religion from a city?

This is an idea I got from planetfall--thanks, dude!

What does everyone think of an option to remove a religion from a city? It would be similar to slavery--morally reprehensible, of course, but historically accurate.

The benefits are that you deny at least 1 GPT and intelligence to a rival if they "own" that religion. It may also help a city resist "flipping" culturally.

But there has to be a balancing cost. It should reduce population like slavery, but without slavery's production benefit. And it should also result in a -1 diplomatic modifier with the religion's home civ every time you do it.

To address the moral qualms many would obviously have with this, unlike slavery where you "destroy" population, what if this sort of "religious persecution" simply sent the population packing? That is, there is a reduction in your city's population, and a corresponding increase in population in a city in the religion's home civ--based on the idea that the persecuted population migrate somewhere more amenable to their wish to practice their religion?

Then to balance gameplay, they could add a pecentage chance that your repression would cause the religion to flourish, spreading even in a Theocracy.

I would say that a given government should be more interested in fighting a foreign religion if it would go against them. It would then make sense to fight them, which would not be the case in Civ4 the way it is. (preventing a given civ to have some income due to religions seems pretty rare and 'unefficient' IMO)

Now, if you want to fight against income provided by religions within your frontiers, you should consider to turn ROPs off or switch to Theocracy.

Talking about your idea, if you can nullify a civ efforts in spreading its religion, it would be a disadvantage for it as it could have built a military unit instead or start the building of a wonder sooner, even with a small pop sacrifice. For the diplomacy modifier, it would not be at your disadvantage if your are stronger than the civ.

And so the (Spanish) inquisition returns ...

"persecuted population migrate somewhere more amenable to their wish to practice their religion?"

There is simply no such thing.