WayneLigon said:
1. Sacred Cow. Wizards can't heal because they've never been able to. Healing and protection and dealing with entities is the main duty of the cleric class. Blowing stuff up is the main duty of the wizard class.
2. There is a traditional anathema between clerical and wizardly magic. Wizards in fantasy and folklore are very seldom seen healing people. Usually priests or wise women do that.
3. If wizards could do that, why can't they do any other clerical spell? Or why can't clerics Blow Stuff Up Real Good? It promotes a definition and seperation between the major spellcasting classes.
It's more 1 & 3 (with "balance" as a reason for 3).
I strongly oppose 2. Healing is not especially divine in nature -- in fact, if you look at how people who studied anatomy were considered in medieval Europe, you could say that the arts of medecine are evil and impious. Wise men and women who knew natural cures were considered like witches (==evil, heretical, and impious), learned men (and women, if they existed) who tried to study how the body works were considered like necromancers (==evil, heretical, and impious).
So, yeah, some hospitalers were gathering the sick in huge dying places where they were all crowded together and would catch all of their buddies' diseases so as to die faster. That didn't make them efficient healers.
Traditional mages could also be considered pagan clerics or druids. Merlin, for example. In less traditional, but still widely accepted, parts of fantasy archetypes... You have Gandalf. He's a wizard. He heals. Remember Theoden's cure and rejuvenation?
The word magus itself is derived from the name of Zoroastrian priests in Persia (modern-day Iran).
The separation of arcane/divine magic is a D&Dism. It's not part of traditional fantasy.
Mages sure can heal in Ars Magica. And in every RPG I've played that isn't copied on D&D.
Finally, a little word about the school of healing. Given that it's the channelling of positive energy, it should be the bringing-energy school, not the bring-beings-&-matter school: Evocation. And most necromancy spells too.