“I think there is a real debate if Foie Gras can ever been kosher because of the way the animals are treated even though it is a kosher animal”
That is utterly incorrect. The question is if they become treifos, not because of some tree hugging attitude.
The halachos of tzar baalei chayim do not change with the times. Almost all the complaints of tzar baalei chayim that all these radical vegetarians hock about are not halachic problems. Why don’t you look up in the Gemara how they used to do shechita of korbonos.
The Gemara talks about the change and tzar baalei chayim never enters the discussion.