The benefit of developing omnivory in evolutionary history provides a greater chance of finding something edible. Like all omnivores, it simply increases the chances of finding something suitable. Just because we can eat meat doesn't mean that we NEED it. Conversely, just because we CAN eat starchy vegetables doesn't mean we have to. I can't remember the last time I ate meat, and nothing detrimental has happened.

Omnivory is simply a straightforward aspect of evolutionary ecology in many species; it isn't particularly interesting and doesn't hold much scope outside of specific scientific hypotheses, and it certainly holds no relevance to modern political aims on sustainability.