Up until about 10,000 years ago, man was a hunter-gatherer. The assumption always seems to be that he survived on the gathering part, while getting the occasional treat of meat when the tribe succeeded in bringing down some food. In fact, those that do mineral analysis of prehistoric bones tell us that our caveman and cavewomen and cavechildren ancestors ate a diet that was about 90% meat.

Then about 10,000 years ago we discovered how to brew beer. This was a huge improvement to our health, because alcohol is a powerful water purification chemical, and so drinking beer, and then later wine, gave us a source of water that was safe to drink. Before that the only source of safe water would have been broths.

So when we started brewing beer, then we started cultivating grain crops to make the beer. And pretty soon we invented bread, which became a staple of our diets that crowded out a lot of meat. We had to create significant property rights -- before this people owned what they carried with them, and so stealing was hard. Once we had lots of real property, we invented war as ways to seize other people's property. And quickly discovered that fighting was a way that you could subjegate others. Women and children were significantly more disadvantaged in the new order -- as hunters they were a far more equal members of the tribe, now they became property. The planting of crops destroyed animal habitat, and the crops had to be protected from the animals tromping through them, so the animals were fenced away from people's property, or they were domesticated. Meat became more valuable, and so access to meat became something that the rich had and their slaves mostly ate bread.

In other words, all of those evil things that the vegetarians are complaining about came about as the direct result of human beings adopting a vegetarian diet. :-)