Opening the book…
Loud criticism usually comes from people who care and have no lever to pull. Left as commentary, it hardens into a faction; converted into responsibility, it becomes the most useful energy in the room. You also learn quickly whether the person wants the problem solved or wants an audience.
Find the thing they complain about most and hand them ownership of it, with a budget or a deadline they can be judged on. Say out loud that you disagree with some of their read and are giving them the job anyway. Then let them do it their way and hold them to the outcome like anyone else.
Do not do this with someone whose criticism is aimed at people rather than problems — you will hand them power over the person they resent. And do not reward outright sabotage with authority; that teaches the whole group what gets promoted.