Actually, I kinda agree. I don't know if it's actually a diagnosable disorder, but I'd say that obsession over total purity is a problem.
Sure, it's a good thing to think about what you eat. It's good to make sure that you eat a range of fruit, veg, grains, beans, etc. It's great to ensure that your diet is not based on nutrient-devoid items like white bread and cakes. It's good to eat organic foods when you can.
However, if you are doing those things--if your diet is made mostly of healthful whole foods, having something 'bad' now and then, like a cookie or a slice of cake, is not going to kill you. If one is at a point where one can't eat a cookie ever because absolutely everything must be 'good', I'd agree that's most likely a problem.
I think that being vegan would be excluded, assuming it's for ethical reasons. That's not about making sure that everything you put in your body is 'pure', as evidenced by the fact that veganism isn't just about food.
I see where your coming from, but whats wrong with wanting are body to be as pure as possibile? I think eatting healthy can be a obsession for some people and it makes them more unhealthy, but you can say the same thing for anything people do. Work is needed to live but you can be obsessed and work 20 hours a day. We know that isn't healthy, but people just call them ambitious. I never touched a drug or alcohol in my life and it was really easy becasue i never tried them. I never obessed about not having them, just the opposite, since i never did them or put thought into it i could think about other stuff
I hear the arugement well eatting that cake or that white flower or that alcolhol isn't going to kill me. Well smoking a cigerett every month or doing meth once a month isn't going to actually kill you, but if has no busisness being in the body so its' best to have none if it. Plus doing bad things once in a while leads to more and more. doing processed foods here and there won't kill you, but living on them like people do sure well.