When you add vegetarianism and veganism to Judaism, it seems like you are making a statement that the Gedolim of the past were somehow not complete in their observance. I say this as someone whose family Minhag is not to eat meat on Tuesdays and Thursdays.
Reducing the amount of meat for health reasons is certainly commendable, but I don’t think our Gedolim overlooked a huge ethical issue which is only now coming to light.