Lots of vegans will try and push this argument, that humans are not technically omnivores. It's complicated, but we know that humans have eaten meat for at least 10,000 years (probably much longer) and our physiology points towards us being omnivorous. It seems silly to say we're not omnivorous, because we can digest vegetables and meat (we have the enzymes present in our gut to break down meat). Just because we don't need meat, doesn't mean we are herbivores/frugivores.

Anyway, I've never thought this argument mattered much, because we know that you CAN survive as a vegan (albeit with a little difficulty). And most intelligent vegans will use another, more compelling argument - The reason, they say, that we shouldn't eat meat is because we know that we don't need it, and we also know that animals are suffering as a result of our meat-eating.

Now personally I think most vegans are shooting themselves in the foot when they try and recruit others, by saying that killing animals is morally wrong. This is because most people won't make such a drastic change to their diet (like many people, I love meat too much to give it up).

What they should be doing, is getting people to eat free-range, outdoor reared animals rather than cheap shitty battery animals. This way, everyone wins - The animals don't suffer and have a happy life, the farmers get paid more, and the consumer gets tastier, healthier meat. If every vegan did this instead of trying to guilt trip everyone into giving up meat, there would be more happy animals in the world.