I just saw an interesting thought experiment by Neil Degrasse Tyson that takes on veganism. Admittedly it's a bit out there but it's still a compelling point. Tl;dr it's basically that if you imagine a species of sentient space aliens that are plant based in that they do photosynthesis for their energy. If they come and visit earth and see these animals (us) specifically targeting plant matter and their embryos (fruits, nuts, etc), they would see us as horrible creatures.

I believe the clip I saw was from his podcast Star Talk. 

 It’s funny, but to be fair, plants very very certainly have a lower level of consciousness than animals.