Pretty much in agreement with you here, although at least the vegans aren't doing any harm - unlike the other extreme.
Will...I would speculate that most vegans are harmless..however though,there is an animal rights organization called P.E.T.A(people for the ethical treatment of animals),which judging from what I've seen from them,are very extremist in their views and actions...which are harmful.
They believe in the total abolition and liberation of all animals(meaning that,for instance),they view owning a pet as being immoral(because to them),that's enslaving an animal.
These people spend their time protesting animal shelters,screaming about how animals are imprisoned,tortured and killed everyday(without giving any thought as to what the real purpose of an animal shelter is for).
These people run around with a campaign against any ownership of animals or the killing of animals for any reason whatsoever,with total disregard for the law,including making terroristic threats towards anyone who oppose their views.
Though these people are adamantly against animal shelters & any sort of animal-based vaccinations or medicines,they actually have their own animal shelter & at least one member that I'm aware of,has used an animal-based medicine for her ailment.
These people are hypocrites & are bat-s**t crazy and there are a total of about 750,000 of them...so I would say that some of the vegans out there are harmful.
http://www.youtube.com/watch?v=GMbLu_HEA3o