Okay I reread Xei's and Taosaur's discussion and thought of something. If everyone gradually became vegan, that wouldn't really save animals in the conventional sense either. What would happen is that less cows, pigs, chickens, etc. would be born in the first place. So animals would only be saved if saving meant not being subjected to life at all.

... Right?

It seems that some vegans/vegetarians think that if they don't buy meat one day, a cow somewhere that is standing in line for slaughter will suddenly be let free. Doesn't work that way.