I think that successful teams may have a place for a "team canary" (?): someone that is going to speak up about points of friction where most others might just end up with apathy and learn to deal with the inefficiency or friction (a "that's just how it is" attitude). Sometimes, complaints are a sign of genuine friction. Complainer may not feel like they have the authority/allotted bandwidth to remove the point of friction. When this happens, give this person some ownership of the friction points and see what happens.
Better to have a free, easy ability to complain about things, and if there is a good manager hanging around somewhere, they can synthesize the complaints and discover if there are solutions possible at the org level, which individual contributors might not know about or even be functionally able to own.