On the one hand, you say that you wouldn't allow it due to flavor concerns, but on the other hand you say you allow everything else from the Character Builder. Are you saying that magma dwarves is the only character option that somehow violates your campaign sensibilities?
We have different tastes. If you like that paragon path, good, excellent, I don't like the idea of barbarians who look like a mix of Ben and Johnny Storm. That's it. It seems that you want to put my "sensibilities" in check just because they are different from yours... =/
I don't mean to rag on you for your preferences, and there's absolutely nothing wrong with not liking the idea of a magma dwarf. Denying your players the ability to make use of it does seem a little off, though.
I call my friends to play in my house. Bought hundreds of miniatures for using with them. Buy the books. Subscribe to DDI. Buy the tiles. Print their sheets.
If something goes against the spirit of the campaign and spoils my part of the gaming fun I'll explain my motives to the players.
Since my first 4E game started the only thing I had to ask, for a more munchkin friend, is that I wouldn't allow a bugbear using a large weapon. By that time the nerf hammer had hit minotaurs and Wotc said that this was something made for npcs to use.
The molten core barbarian would be the second "no go". Some people forbid tieflings and dragonborn... compared to that kill a paragon path is not so horrible.
And the player has ALWAYS the opportunity to refluff if he likes the mechanics.
However, I would never have compared it to Magmaman (seriously, Avin, Magmaman? I'm looking at that picture and I'm not even sure how you get that)
You want to say that I made up that example just to piss off the people who like the paragon path? Come on, Allister... if I wanted to piss 4E fans (nonsense, I'm a 4E fan myself) Ragnarons or some other World of Warcraft (also a Wow player) mob would be the perfect choice.
I love Megaman. Megaman III is my all time favorite video game. I had already killed 4 bosses, including Gemini, when I found Rush (the dog). A game where Start and Select do tricks? Fantastic! Do you know what is like to get to Gemini without Rush?
It's a MAGMA dwarf, dude, and that was Magma Man. Maybe you're limiting to image association to artwork, I'm thinking about essence.
I don't even know why this is so polemic.