Actually, clouds are the most effective of the greenhouse gases. If you want a warm winter night or a really mugged unbearable summer night, there is nothing like cloud cover to do the trick.
I would not go around calling people morons unless you are sure you know what you are talking about.
Water vapor is indeed the most effective and most active greenhouse agent by far.
Clouds OTOH, operate to counteract conversion of visible spectum into heat at the surface by reflecting radiant energy back towards space.
Low cloud layers induce net cooling as both daytime solar radiation and atmospheric heat in the form of IR above clouds, are reflected upward to space.
A consequence of that reflectivity is that night time losses in the heat balance are not made up in the daytime influx of solar energy interacting at the surface which would otherwise heat the greenhouse gas components in the atmosphere.
High altitude ice clouds also act as a very efficient reflector of visible solar spectrum again inducing net cooling at the surface by intercepting incoming solar energy that sets thermal equilibrium of the atmosphere.
Cloud interactions are very complex and poorly accounted for in current climate models. Therein lay the weakest links in the Global Warming rationale.
Clould also reflect light and prevent heat from reaching earth. At night time it serves retain heat, but not during the day. The long term effect should be a net cooling.