I'm confused about where the debate is... 

I think this 'subtle' magic is impossible to keep out of the RP. If someone wanted to be a witch of sorts and read palms and brew potions, nothing is stopping her. The only thing is that her potions won't make someone turn into a frog. She can't see the future exactly nor can she read minds or people's past. They can, however, make someone sick (poison) or maybe help them recover from illness (hello penicillin). She can make things disappear and reappear with slight of hand and such. In fact, I read tarrot in real life. I know how it works and if it can make people believe its real in real life, well, it should work in this world. 

So, the only thing that is being debated is if things that do NOT work in this world will work in the role play. It seems that most people are against this though... No throwing fire balls or calling lightning. Soooo again, where is the debate?