Vampires, of course, feed on something that we desperately need but also can't imagine being a source of food.
You have metaphorical vampires in your life. These are people that feed on negativity, on shooting down ideas and most of all, on extinguishing your desire to make things better.
Why would someone do that? Why would they rush to respond to a heartfelt and generous blog post with a snide comment about a typo in the third line? Why would they go out of their way to fold their arms, make a grimace and destroy any hope you had for changing the status quo?
Vampires cannot be cured. They cannot be taught, they cannot learn the error of their ways. Most of all, vampires will never understand how much damage they're doing to you and your work. Pity the vampires, they are doomed to this life.
Your garlic is simple: shun them. Delete their email, turn off comments, don't read your one-star reviews. Don't attend meetings where they show up. Don't buy into the false expectation that in an organizational democracy, every voice matters. Every voice doesn't matter--only the voices that move your idea forward, that make it better, that make you better, that make it more likely you will ship work that benefits your tribe.
It's so tempting to evangelize to the vampires, to prove them wrong, to help them see how destructive they are. This is food for them, merely encouragement.
Shun the ones who feed on your failures.