If you don’t have a contrarian in your group, go find one.
Contrarians are those people who doubt everything, question beyond reason, keep pushing for more explanation. They stretch out discussion when you just want to get some damn thing done.
Contrarians aren’t always just plain negative, but sometimes they really are. When that is so, they need to go find work elsewhere.
Mature managers know how to handle the entire range. They understand the importance of listening before acting, seeking to understand what drives a person’s beliefs. Sometimes complainers benefit from explanation, sometimes they just need a respectful listener.