1) As much as belief in magick and spells is a key factor, I would not say that the belief part applies to all. Yes, any one can cast a spell, but not all believe in it, yet can still cast. Any one, whether having prior knowledge to or belief of up to the present (if up to the present with belief) cast some type of spell without even realizing they are doing so. It's really just about an every day thing.
2) it doesn't matter whether magick should or should not be used to harm a person. Any spell can backfire. Any spell can cause some amount harm to a person. Whether for the intent of harming or not; any intent really. So to protest against magick that is intending harm would be a pointless matter. And if you do so, you might as well protest against magick as a whole and not pick out specific aspects to be against. What then when you try to do a healing spell (for example) and it backfires in some way and causes that person more harm than help? That would then be a spell that once was a helping spell, now turned harming. Now we have to veto healing spells. Again, a pointless matter of saying what should and should not be done with magick that can be done. Despite what it seems like on merely looking at it, you can find plenty of good and helpful ways with spells that cause harm, such as cursing. In many cases it takes some amount of harm before healing can be done. Just like you can find many harmful aspects of a healing spell despite what it appears to be. Truly, harmful spells are no better nor worse than helping spells.
3) We are all psychic to some degree on some psychic ability. Though each person can be more naturally skilled with a psychic ability over the rest. It's what we do with the potential that we have with such abilities that governs whether they can be done or not. Whether you're natural at one or not, they can be learned and developed.