If you are a PvE mage in classic, you shouldn’t stand in melee range (it increases your threat) and you should get any threat reduction talents and the Subtlety enchant.
That said, a mage pulling aggro is not a problem if they can handle it. If they can kite the mobs around and it doesn’t result in loose mobs, adds, or higher incoming DPS than a tank standing there taking it all through their steel suit, then it is a win.
If the mage is getting insta-crushed, mobs are splitting up into groups of one to teach your healer a particularly brutal lesson in the fine art of multi-tasking, or the healer’s mana pool is being drained through a cloth sieve, then it is a loss.
In classic, a mage can pretty easily pull aggro even with single target. One advantage there is that a tank’s taunt right after a mage’s aggro pull will generally buy the tank a good bit of time to build threat ahead of the rest of the group. Frost mages are particularly nice for this because ice block provides insurance, if necessary.
Ultimately, the ideal is minimizing incoming damage and maximizing outgoing damage. Kiting mobs does a better job of minimizing incoming damage if it is controlled. It may or may not maximize outgoing damage depending on group composition and discipline. Either kiting or traditional tanking may be more favorable than the theoretical ideal depending on group composition and individual character horsepower.
I guess the bottom line is this: if a mage can pull aggro and benefit the group by doing so, then do it. They just need to be able to handle it and communicate what they are doing to the group. Generally speaking, it is a more suitable tactic to dungeons than raids (there are a few places in BWL and AQ where you can let a mage loose). As a tank, I would be open to it as a legitimate tactic and try switching your focus to catching loose mobs (look for mobs outside AoE, healer aggro, or ones taking a lot of single-target/snares/stuns from that damn rogue) and dropping some tank-deeps. If the mage can’t handle it, switch back to old school.
EDIT: Mages don’t have a threat dump in Classic but, aside from that, they don’t generate any more threat per unit of pre-talent damage than other class. They just hit like a truck. This is a good thing so long as the mage can restrain themselves or use it to the group’s advantage depending on the situation.
