When the plan fails the problem won't be perceived to be a bad plan. The problem will be perceived to be that the worker bees did not correctly implement the the bad plan, hence the failure. This is especially bad if you expressed misgivings about the plan ahead of time because it will be perceived that your negative attitude and lack of confidence in the plan were key to its failure.
I keep using the word "perceived" because, in situations like this, the perception is what counts, not the facts.
I've tried this tactic in meetings - simply keeping my mouth shut while the idiocy reigned supreme on the projector screen. Sadly, there's always that one clueless person in the back who doesn't realize that we all KNOW it's crap and feels it necessary to inform us, thereby extending the meeting time to an eternity of useless debate.