Människan - växtätare/allätare, förmåga att bryta ner cellulosa?

Mitt svar på påståendet att människan inte är en herbivor/växtätare eftersom hon inte kan bryta ner cellulosa.
Människan är en växtätare:
http://bloganders.blogspot.no/2013/06/humans-are-herbivores-not-omnivoresmeat.html

Mitt svar:
 Why would you have to digest cellulose in order to be a herbivore.

Humans digest starch:
Through genetic testing scientists have proven that we are obligate starch-eaters.2 Examination of the number of copies of the gene for the production of amylase, an enzyme in our saliva that digests starch, has found an average of 6 copies in humans (range of 2 to 15 copies), compared to only 2 copies of this gene in great apes. This amplified number of gene copies allowed early humans to thrive on starchy foods that “lesser” primates ignored. The diets of great apes, like those of chimpanzees, our closest relative, are nearly pure vegetarian in composition; consisting largely of fruits, and in the dry seasons when fruit is scarce, they eat tree seeds, flowers, soft pith, and bark; with termites and small mammals making a very small contribution all year long. Chimpanzees eat very little starch.

Human and chimp DNA is roughly 99% identical, but that 1% difference, which includes genes to digest much more starch, proved crucial for the evolution of humanity's earliest ancestors. More salivary, starch-digesting, amylase produced by more copies of the gene opened up a reliable supply of sugar for our early ancestors, which allowed their sugar-fueled brains to develop. Twenty percent of our daily food intake is used to energize our brains; and brain tissues preferentially burn sugar for fuel. The theory that the addition of meat or fish to our ancestor’s’ diet was the critical factor for the development of our ancestors’ brains is obviously incorrect based on our physiology and genetics.3-5 Furthermore, since most early humans ate meat only sporadically, meat alone could not have supplied the extraordinary amount of energy needed for the brain to grow from monkey-size to human-size (three times difference).3-5
http://www.drmcdougall.com/misc/2008nl/jan/grains.htm

....
But, this isn't relevant to the moral discussion. The only thing relevant is that we can live and thrive on a vegan diet. And it is morally wrong to consume animal foods just for "pleasure"/convenience -- which is the only justification you can provide.