This brings up a more general point about the dangers of blocking
everything under the sun. When you limit yourself to just a few
chokepoints, its easier for those who would stifle communications
to shut things down.
This is a very dangerous path to take. Not that we shouldn't consider
some sort of port restrictions to stop spam, but there are undesirable
long term effects that need to be considered. Those on the dark side
will be "considering" them, you may be sure, while licking their chops.