Speaking of things that will proably eventually kill you...

[GenuineRisk]

Human beings are generalists- we can survive on a wide variety of foods, which is one of the evolutionary attributes that assisted us in becoming the dominant species (as far as vertebrates go, anyway). If you look at humanity all over the world, different cultures have vastly different diets (there are some where the main diet is milk), depending on what's available. And humanity thrives, not just in the industrialized West.

Speaking as someone who was a strict vegetarian for years, it doesn't make your hair and skin go dull. I started (occasionally) eating meat again just because going out to eat got very boring as most restaurants don't put much thought into non-meat entrees.

I didn't notice any difference in health when I was eating (factory farm) meat at every meal to when I was a vegetarian, to now, when I occasionally eat only humanely raised meat (which means grass fed if it's beef). Honestly, and this is purely anecdotal, as it's just me, the only food I notice actually making a difference in my diet is fresh fruit (higher fiber ones). Which I hate, because I have texture issues, but when I'm good about eating it regularly, I really do see a difference in energy level and mood. I ate a lot of it when treating my gestational diabetes and felt GREAT.

Homo sapeins are generalists. We can thrive on a lot of different diets. That said, I do agree with everyone here that processed food is nasty and the less of it in a diet, the better. I don't think evolution has caught up with high fructose corn syrup.