Personally I think a lot of the issues that ever arise between player and GM tend to revolve around the fact the players "forget" that its the GM's job to tell a story. It is after-all their story to tell and the players are the characters in the story. In the last nearly three decades of gaming I have seen more than my fair share of players and GM's who nit pick at each others roles and its just absurd. The players should focus on playing and the GM focus on story telling. Simply put if either party doesn't like the way things are going then there is the door.
As a player I can say there have been countless times I have not been fond of how things turned out in a game or a campaign and for the most part I have been good to just accept on faith that the GM knows what he is doing. Of course a little nudge of help with rules or style have been given to new GM's but over all its their style and their story to do with as they see fit.
More specific to the issue of the Original Poster... as a GM I have many house rules that I use in my campaign such as Paladins being a Prestige class requiring 1 level of fighter and 1 level of cleric. With that said banning a class isn't really all that "out there". Granted doing so for the reasons you gave seems silly to me but is there a chance he said that simply because the GM didn't want to discuss it for fear of giving something away in the story? Perhaps barbarians are banned because there was a recent culling of the barbarian tribes by the evil king?
One of the things I make very clear to my players before they play is that I do not subscribe to what i call the "Everquest style of play". You don't walk out of town and only fight creatures you stand a 99% chance of winning against. If you go looking for trouble you will most likely find it. With that said when I write adventures and scenarios i write them in the point of view of the bad guys. If its something they should know... they will use it. If there is magic treasure in their horde... they will use it. There will doubtfully be unguarded ways into their camp (without some reason for it)... etc. I have had several players take issue with my style and i have been happy to talk about it but ultimately there is a reason for everything I write so getting upset that creatures have powers not listed in the bestiary... too bad.
Players shouldn't know that information anyway unless they have done extensive fighting or research of the creatures.
Now I am not saying the GM is without fault here. It is after all his job to make the story fun for the players to be in, but Seto I ask you... why exactly are you upset with the GM? Is it because the GM isn't letting you have your way? Or is it because his style is making it impossible for players to have fun? I say this because it is often a misconception in the disagreement between the GM and player.
I will give you an example of one of the last group crushing arguments my table has had. The group had arrived at a small border town returning children they had rescued from a goblin encampment where they were being used as slave labor in mines. When they arrived the farmers were glad to have their children back and seeing these bigger than life hero's here in their town... asked them to help clear some ruins infested with lizardmen that had displaced the goblins that took the children (the PC's didn't know this fact yet). Without doing any research or investigating the PC's just charged into the ruins and proceeded to get arses handed to them in a very naught fashion. Three of the five members got mad and said that the fight was unfair and there was no way they could win. Most likely that was true considering their approach to the task.
The point is it was just one way of doing things and at that, the worst way since that is what the bad guys had anticipated. Sometimes the GM actually thinks ahead and gives detail to an adventure. Players cry foul... while the GM cries "willful ignorance"...
EDIT:
Before I forget. The going out of the way to kill one character over another... perhaps the bad guys are smart enough to pick out the biggest threat. In my scenarios if the enemies are intelligent they often take out spellcasters first knowing they include healing and mass damage support. Wizards in my games have learned to use tactics and positioning to better effect... which is ultimately something that has made them better players.
