Flaw-foodists.

Veganism is biologically unnatural, logically and morally flawed.

Vegans claim to love nature and that is the reason they do what they do, but they confuse nature with animals alone. Otherwise there would be a plants rights movement (or atleast a serious one). Personally I love nature so much I want to live as naturally and inline with my natural biology and environment as possible (within reason) and thus I'm omnivore, also you can't be vegan and natural / organic because the vital vitamin b12 would have to be replaced by a man-made synthetic. Vegetarians can, but vegans can't, also you can't raise a baby on a vegan diet as there is no comparable substitute to milk proteins. 

"WHEN Crown Shakur died of starvation, he was 6 weeks old and weighed 3.5 pounds. His vegan parents, who fed him mainly soy milk and apple juice, were convicted in Atlanta recently of murder, involuntary manslaughter and cruelty."..."Protein deficiency is one danger of a vegan diet for babies. Nutritionists used to speak of proteins as “first class” (from meat, fish, eggs and milk) and “second class” (from plants), but today this is considered denigrating to vegetarians. The fact remains, though, that humans prefer animal proteins and fats to cereals and tubers, because they contain all the essential amino acids needed for life in the right ratio. This is not true of plant proteins, which are inferior in quantity and quality — even soy." http://www.nytimes.com/2007/05/21/opinion/21planck.html?_r=0

If we were to subscribe to the ideals of veganism then we'd throw away our computer, the plastic that makes it is an animal product caused by the decomposition of animals into oil. We'd take our chance with diseases and give up all medicine because at some stage it was tested on animals.
You might say this is incomparable, but if you are "not going to use animal products" then don't be a half assed hypocrite, don't use ANY animal products, do it right or not at all. And you may say meat is immoral but the majority think this is only because of the death factor, something still died to make your luxuries.
Vegans will claim animal rights, (and I will too, death doesn't have to be a drawn out torture. Infact I think the cruelty and immoral act is the poor conditions the animals LIVE in, death is nothing compared to low welfare intensive farming). Vegans will claim that animals are equal to humans. And YES they are.

Do you know why animals are equal to people? Because people are animals too, biologically programed and evolved for and omnivorous diet. Competition and death are a part of nature. If you don't like it then you don't love nature enough to fully accept it, and you aren't tough enough to function in reality. Nature is brutal, it needs to be in order to function, but it is not a valid reason to give up aspiring and adhereing (as best you can) to what is natural.
You could be vegetarian (different to vegan) and still live naturally, vegan (specific) diets  are so unnatural they kill people and make them ill. You don't need more than half a braincell to work out that means veganism is illogical at best and downright dangerously incompatible on a biological level at worst.

"If it were not for humans eating meat, specifically cooked animal flesh, our brains would not have developed (http://www.npr.org/2010/08/02/128849908/food-for-thought-meat-based-diet-made-us-smarter) to the point where we could start making freeways and breakfast cereals and digital video cameras capable of recording two females and their adventures with a cup."

Read more at http://www.bullshido.net/forums/showthread.php?t=115052&s=08f58289bc741cc310b5699b3c88ce2e#S8gLabBYGFtliXih.99

"From habitat destruction to combines that inadvertently mince rabbits to the shooting of deer in farm fields, crop production is far from harmless. Even in our own organic garden, my wife and I were battling ravenous insects and fence-defying woodchucks. I began to see that the question wasn't what we ate but how that food came to our plates. A few years later, my wife -- who was studying holistic health and nutrition -- suggested that we shift our diet, and my health improved when we started eating dairy and eggs. It improved still more when we started eating chicken and fish. Two years later, I took up a deer rifle." http://www.theatlantic.com/health/archive/2011/12/eating-animals/250179/

As you can see babies have died of veganism and it's not recommended for pregnancy either, it interferes with one of our most basic functions as living beings (to reproduce) you don't need to be a genius to figure out from that, that humans are not meant to be vegan. If the world was to end tomorrow, all power and factories, and man made technology shut down, and nobody produced their supplement pills anymore. When the malnutrition sets in, and they realise they are starving to death will they give in to their hypocrisy and eat the squirrel? Or be too snooty to love nature in all it's imperfect glory and become a victim to natural selection? Put simply Veganism is unnatural (or atleast total FAIL), because those unwilling to diversify go extinct.

“It is not the strongest or the most intelligent who will survive but those who can best manage change.” - Charles Darwin

Source:Imperial Cancer Research Fund, Cancer Epidemiology Unit, Oxford, United Kingdom. key@icrf.icnet.uk 

Abstract;

We combined data from 5 prospective studies to compare the death rates from common diseases of vegetarians with those of nonvegetarians with similar lifestyles. A summary of these results was reported previously; we report here more details of the findings. Data for 76172 men and women were available. Vegetarians were those who did not eat any meat or fish (n = 27808). Death rate ratios at ages 16-89 y were calculated by Poisson regression and all results were adjusted for age, sex, and smoking status. A random-effects model was used to calculate pooled estimates of effect for all studies combined. There were 8330 deaths after a mean of 10.6 y of follow-up. Mortality from ischemic heart disease was 24% lower in vegetarians than in nonvegetarians (death rate ratio: 0.76; 95% CI: 0.62, 0.94; P<0.01). The lower mortality from ischemic heart disease among vegetarians was greater at younger ages and was restricted to those who had followed their current diet for >5 y. Further categorization of diets showed that, in comparison with regular meat eaters, mortality from ischemic heart disease was 20% lower in occasional meat eaters, 34% lower in people who ate fish but not meat, 34% lower in lactoovovegetarians, and 26% lower in vegans. There were no significant differences between vegetarians and nonvegetarians in mortality from cerebrovascular disease, stomach cancer, colorectal cancer, lung cancer, breast cancer, prostate cancer, or all other causes combined.
^Vegans do not live the longest.^ http://www.ncbi.nlm.nih.gov/pubmed/10479225

As for your "moral obligation" and a plants rights movement?

"She said: ‘Everyone knows that plants react to light, and scientists also know that plants use volatile chemicals to communicate with each other - for instance, when danger , such as a herbivore, approaches.’

Dr Gagliano said the research ‘opens up a new debate on the perception and action of people towards plants’ which are not objects but should perhaps be treated as ‘living beings in their own right.’"
Read more: http://www.dailymail.co.uk/sciencetech/article-2157221/Maybe-Prince-Charles-right-British-scientists-reveal-plants-really-talk.html#ixzz2KOxW1A3D

If we looked at the evidence, that plants can show fear we can rationalise because they react to damage they must ergo/ subsequently feel pain. But nobody gives a shit about them or fights for their "right" to not be eaten, because plants aren't cute and don't bring in good money or publicity.
And we see the same in the animal world, almost everybody loves Fido and Mittens but everybody given the chance would also have a bug zapper.

See also:
http://letthemeatmeat.com/post/3141542244/interview-with-an-ex-vegan-tasha
http://www.didyouwonder.com/do-plants-feel-pain/