TCG,
I once heard Harav Avigdor Miller A”H talk about this topic, This is what he said.
The activists have a point, they are right! according to logic man has no right to kill animal. However, Hashem has told us otherwise that is why Jews have permission to kill animals for food.
IN other words, an atheist or anyone that does not believe in the Torah, has no permission to kill and eat animals, it is only the word of Hashem that permits us to do so.