Most companies have their share of employees who like to complain.
At one company at which I was a manager, we had a small cabal of malcontents that constantly moved about with dark clouds of bitterness over their heads. These people could find something wrong with anything—management, their co-workers, the vending machines, you name it.
In group meetings, these people would exchange looks, murmur to each other, or just smirk at random. It was very disconcerting to be delivering a presentation and be able to see two people passing judgment on you. It was passive-aggression at its best/worst, sort of like tripping over something in front of a group of high school girls. But no matter how many times we approached these people directly, we could never get any useable feedback. All we'd get was a bunch of blank faces and denials that there were any problems.
Now there are a couple of dynamics going on here. First, some people are just pessimists who get (what passes for) joy from finding fault with everything. Maybe it's a result of low self-esteem—tearing down others somehow builds them up. It could be a result of too much self-esteem—nobody can possibly live up to their standards.
It could also be that management is truly making mistakes. But even if your company management is the Larry, Curly, and Moe of the business world, you gain nothing by talking behind their backs. Thoughts, even hateful ones, do not magically make their way across the room into the consciousness of other people. Management, or anybody else for that matter, cannot mend mistakes unless they know what they are to begin with. Maybe I speak for myself, but I would much rather someone come to me directly and tell me about a problem (no matter how awkward or painful the encounter is) instead of ridiculing me behind my back and letting the problem fester. I realize that there is the fear of reprisal or that your manager will hold your words against you. But there are ways to state things where the blow is not as visceral as a dismissive eye roll from the back of the room.