Why Not Invade Cuba?

Really, why aren't we invading Cuba? I know that posing such a question is a standard pacifist tactic, to extrapolate from whatever our current imperialist enterprises are to the whole world, but in this case I would really like someone to explain why we don't invade Cuba. Cubans are subject to a ruthless dictator, their defenses are weaker than Iraq's, and they pose a much more serious (potential) threat to the US than people in the Middle East.