The objections to helping the rebels in a small way are mostly to the effect of "all or nothing"; we land the Marines or we do nothing at all. The logic motivating this is that if there is an immediate critical national interest at stake, we do all and if there is not, we do nothing. A corollary of that position is that if we do anything, we will inevitably do all; all or nothing again.
I wouldn't characterize it that way at all. First, what is the objective? Do you know? I sure don't. The use of military force must have a purpose - what is that purpose? "Doing something" without a goal is worse than stupid. The level of force required completely depends on what we're trying to do.