Most of the people who read this knows of my work at an environmental NGO and I think there's such a big fuss about how environmentalists ought to be vegans. I for one am not vegan because I believe in biodiversity and in symbiotic relationships in the ecosystems, if veganism is really the natural way of how things work it would then be tantamount to saying that lions behave 'un-naturally' because they hunt and eat meat of their prey (hence there's a symbiotic relationship between the lion and the prey). Just now I stumbled upon another insight about veganism and why I am not a vegan, another is that veganism is a consumer activity here's a portion of an interesting article about veganism from Infoshop:

Thus, a vegan diet may be seen as a sensible response by people who want to minimize their involvement with the meat industry in an industrial capitalist society. But this is not a universal context, whereas veganism markets itself as a universal solution. PETA has declared that you can't be a meat-eating environmentalist, and most vegans believe this line or toe it explicitly. What vegans have failed to think out is that industrial capitalism has not existed forever, nor have human societies always been ecocidal or abusive towards animals. In fact, to avoid eurocentric conclusions vegans must admit that the first and the very best environmentalists eat meat. I refer to a number of indigenous societies, past and present, that have the best track record of living in harmony with the environment and seeing other species as their extended families. Especially since vegans put so much emphasis on the impacts of an individual's lifestyle, they (being nearly all residents of wealthy countries) are deluding themselves and the broader communities to which they advertise their image as the preeminent environmentalists, considering that these omnivorous non-capitalist societies had a much lower ecological footprint and a much deeper affinity for animals than anyone socialized in an industrial society can ever gain in their lifetimes.

Read more about it on this link