I did read it. I also try to stay abreast of points of view that counter my own. I'm yet to find any seriously compelling evidence, but that doesn't mean that I don't look.
I don't back down from the arguments I've made for veganism, the getting your points was re: the ED stuff. It doesn't have the scientific research behind it to be proven, but is all plausible. Since the initial ED post was primarily a reaction to being trolled, I didn't feel the need to go too in depth attempting to defend it.
I agree many vegans are pretty invested, and it often manifests in ugly fashion. You're painting a pretty thick brush if you include me in that, I've been pretty even toned.
To answer your question, many vegans get seemingly disproportionately involved because to them it isn't simply a choice about health. To most vegans it comes down to this. "Can you be as healthy and as fulfilled on a vegan diet as one including meat?" If the answer to that is "yes", then why the **** are we ruining the planet and doing seriously morally questionable things in animal agriculture?
(Animal agriculture being the leading cause of greenhouse emissions, deforestation, ocean dead zones etc...
http://www.cowspiracy.com/facts/ for a glance at some of the environmental arguments. The moral arguments essentially boil down to does an animal suffer more in the creation of meat than you benefit from its processing).
While it is possible to maintain a fairly zero sum argument with pro/anti the complete elimination of meat products from the human diet, the moral and ethical arguments are decidedly more one sided.
Obviously, that's not what is being argued in this setting, but it is there.
Then take into account the amount of undeserved derision vegans face throughout society, couple it with the farcical pro meat arguments often flung our way (like claims that if we don't eat animals they will overpopulate and take over the world) and you'll get some more understanding why many seem highly strung.
Happy for you that you're staying healthy. You won't hear me argue that veganism is the only way to achieve health.