In my opinion, animals like cattle and deer have feelings. Unlike animal meat, most plants do not have Vitamin B12, which we can't produce without B12-producing bacteria in our gut.
The human colon isn't really made for herbivorous diet. You need to eat all sorts of plants that probably have to be imported in order to get the nutrients you need, unless you can grow a decent garden. If we were rumiants, then that would be a different story. (we couldn't eat meat at all if we were rumiants, or in general with a herbivorous digestive system) Read BubbaGum's post. I'm going on a neutral opinion. I won't become vegan until scientists find safe ways to convert our digestive system into a herbivorous one.