"'I will come to you in the black of some terrible night and I will bring a pointy reckoning that will shudder you . . .. I can make you wish you had never seen the sun go down!'" -The Crucible by Arthur Miller
Not everyone in a fantasy setting trust in Magick. In some cultures it can be a dark evil thing that is best left alone! You could find yourself becoming the slave of some creature of the beyond that you sought yourself to enslave. Spells can go wrong and who will pay the consequences. Mankind was not meant to dabble in forces that are beyond our comprehension and control.
I'm a fan of 60's and 70's horror movies, especially the ones involving witchcraft. A couple in particular that really stand out are Witchfinder General and Mark Of The Devil. These movies are great fodder for role playing games!
You could play a cleric character as a religious zealot, who serves a deity trying to cleanse the world of magick and sorcery. Purging sorcery in the all cleansing flames of righteousness.
You could also be a character who's family was killed by practitioners of black magick. Sacrificed by some dark god or evil demon. Now they will meet justice at the end of your blade!
Or you could be a sort of enforcer used by the guild of Wizards to root out those who haven't paid their dues. Wizards can be every bit as vindictive as the mundane world can be. Especially if there's money involved!
Just a few random ideas to make a campaign interesting!
Keep rockin' & Role Playing!