This could be a situation where nobody really likes the outcome, but (since it was obviously a very fair punishment) they all treated it with respect (wanting to signal that they liked it). So nobody suggested anything really exciting, figuring that nobody else would go along with it. (There's a name for that fallacy of decision, where everybody votes for their second choice to be nice, since they think that it's the first choice of everybody else.)

Or else, they each had a secret plan (to summon Harry to their arms).