Perhaps combust is just a bit confused by the fact that some people voluntarily limit their diet and annoyed that their minority choice is expected to be catered for.
I am in the unfortunate position of having certain food intolerances (thankfully no anaphylactic reactions, but extremely unpleasant and painful ones, nonetheless). My diet is a PITA and I wish nothing more than to be able to eat whatever I like. This would make travelling and eating out at restaurants and friends' homes so much easier and more pleasant.
I have several vegan friends and most are vegan either because they are ethically opposed to eating other animals or animal produce (partly because of concerns over animal welfare) and/or they feel that mass production of animals to feed human demand is environmentally unsound and/or they feel it is 'healthier'. Perhaps there are also other reasons for choosing veganisim, but these are definitely the most common ones.
I find it inconsistent that if you are ethically opposed to eating animals due to mistreatment of animals that you could also wear leather or use leather products or feed your own pets products with animal derivatives yet many of my friends do.
I find it strange that those who feel it is 'healthy' to be vegan consume so many processed foods (the trusty 'vegan substitutes') and require vitamin supplements to make up for nutritional imbalances.
I find it hypocritical that those who choose veganisim for 'environmental' reasons fail to realise that most of the fertiliser used for growing fruit and vegetables contains animal products and that the arable land required for the quantities of plant material to grow is substantial, and cannot be used more than a few times without fertiliser or the land becomes barren. Also, a number of vegan products (as also do non-vegan products) contain palm oil. The demand for this particular product is responsible for the destruction of a great deal of orangutan habitat in the world and mass deforestation.
I have the utmost respect for someone who is consistent in their beliefs and practice, but this is sadly rarely the case. Read a brilliant article lately about an ex-vegan who had realised that the basis of which he had chosen veganisim was substantially flawed and he resumed eating an omnivores diet. His main realisation was that there is a lot less difference between animal/plant produce and the food chain than he had thought when he chose a vegan diet in the first place.
Or perhaps the main problem with veganisim is that someone who hasn't chosen it for themself, just finds it difficult to understand difference!