The Premise
Being passionate about something is great, especially when it's for a positive cause. In the case of living a Vegan lifestyle, the feeling of actively making an effort to make the world a better place everyday can be indescribable at times; considering the evidence which suggests that a Vegan lifestyle could actually save the planet, some would argue that adopting it should be the first step for all the aspiring environmentalists out there.
How could such a benign principle possibly go wrong?
The Problem
Well... it seems to me that being overly passionate can come at the cost of tolerance towards those who share a different worldview. It's easy to slip into the dark side, demonizing every "omnivore" you come across, especially those who claim to be environmentalists. Even though this clearly shouldn't be the token response from Vegans, it isn't obvious to me that such behavior is entirely wrong... So, where's the middle ground?
Where Do We Go From Here?
In my opinion, leading by example is the best course of action. People need to feel as though they're making the change for themselves, and not because someone told them to. Additionally, Veganism is predominantly about compassion, so it seems morally inconsistent to advocate for the safety of all animals and be hostile towards your own species at the same time. People will listen if it's in there own interests eventually, give them time.
Some people can over do it sometimes
But what would happen if everyone became a vegan, at least pigs would become superfluous what would become of them, would they just be let loose in the wild, then a wild animal can eat them? Same goes for cattle, their only use is milk and meat and hides, so if a cow no longer gives milk, or you have too many bulls, what do you do with them? Maybe these species would disappear so as everything veganism has some good things but it also has some flaws, I don't see it as a planet saver.