Banning a class outright isn't always bad.
Psionics isn't always allowed at our tables because the GM (depending on who is running at the time) doesn't always want to learn a new subsystem, especially if it is from a book he doesn't own a copy of.
Summoners are often banned due to the large group size. Summoning specialists are also disallowed for this reason.
Gunslingers are banned from one game due to it taking place in the Forgotten Realms (where no gunpowder is stated, replaced by incredibly expensive and obviously magical smoke powder).
Only the Summoner ban seems to be maintained from game to game (and even that isn't 100% of the time, other nights with smaller groups allow it in), Psionics and Gunslingers have made it in in several games. Our group's first question when Skulls and Shackles was proposed was whether or not guns and gunslingers would be in play for the party. Pirates, at least to us, inspires images of the Golden Age of Sail, and that means firearms.