Why? Well, the reason most commonly given is that you spent the last few months raiding and equipping that mage, and it would be unfair to retire the mage and start over as a rogue. After all, the guild has equipped that mage, and all that loot would be wasted. I totally get that point of view, and it is a reasonable one. I mean, if you let one person change their class, what if everyone does? That would really kill progression. However, some of the folks who want to change mains see it a different way. They want to change because they are bored, and isn't playing a game supposed to be about the fun? And from another point of view, you are running the risk of losing the mage-wannabe-rogue if he gets fed up and rerolls on another server. If a player is fun to have around and not a drama queen, why not give into their wishes? Is it worth losing a good player over 4 pieces of tier 2 gear? I can really see both sides of the issue.
With that said, I have never been in a raiding guild that allowed someone to switch their main under any circumstance, and in talking to some of my friends today, neither have they. Once you roll on that first piece of BWL or MC loot, you are essentially committing to your character for the rest of your tenure with the guild.
And another thought, with The Burning Crusade right around the corner, wouldn't now be a perfect time to allow folks to switch mains if they so wish? By the time everyone regroups at level 70 to start endgame raiding, most, if not all, of your current gear is going to be replaced. That means, provided the guild has a good balance of classes, that the switching of the main is not hurting the guild or "wasting gear." Of course, you'd have some folks raiding with new classes, and there would be a learning curve with that, but that is to be expected. And with all the new talents, spells and encounters, there would be a learning curve anyway.
So what do you guys think? Do any raiding guilds allow the switching of mains? And if they do, how is it handled? Finally, is the expansion release the perfect time to switch classes without a penalty?