It's just as easy to jump to the opposite conclusions: a bad apple makes a group question the validity of its goals. A group who spends time making sure its goals are worthy is bound to be less productive, but is more likely to do the right thing.
I found myself breaking the rule and complaining about East Coast weather a lot. So I then amended it to, "I hate this weather. I'm moving to Spain or California in the next year", then I took gradual steps to set myself up for it. Then I went to Barcelona, spent some time there, and now I'm in Los Angeles. "This project seems to be sucking huge manhours - I wonder if there's a way we can outsource the real grindwork here?" --> Very, very cool. "This project seems to be sucking huge manhours. I hate this. This sucks." --> Totally not okay.
If they're skeptical of your idea or whatever, they should add constructive input instead of dragging on everyones spirits.
Though I admit, it would be weird if someone can tell an idea is bad, but not be able to say why. In that case I think the detractor deserves to be ignored on the grounds of insufficient proof.
All you can say about bad apples is that they point to a problem. To fire them without asking is shooting the messenger.
Certainly seems consistent with what I have experienced (I see myself falling into the "depressive" dysfunction from time to time, and I know plenty of people who could be #2).