If, as per the OP, wizards are shunned for an unnatural approach to magic, then I think that spells should manifest (at birth? at puberty?) in each NPC according to unknown (but widely debated) mechanisms (the will of gods, bloodlines, random mutations). (For PCs, players get to choose, but assume the PC was destined that way). If all this were true, then it would justify why wizards are shunned for calling upon abomination magic that doesn't occur naturally from within.
Another logical conclusion to - naturaly manifested magic - would be breeding programs (both "legitimate" and not so legitimate) both for power level, and for producing specific types of abilities. It would also mean that nobles (particularly kings) would be extremely careful about who their children breed with - and nobility may be based on magical ability in addition to the usual wealth and money standard. And lead to some interesting scandals - such as the crown prince having the wrong type of magic and/or not having powerful enough/any at all etc.