The way duality works, even pure radiant light can burn and harm. No spell is truly impossible to have go awry, but I do not believe your worries are either unfounded or invalid.
Many people are drawn to darker paths before finding their proper ones, simply because in our society dark is deviant.
However, simply because this is true does not make all dark magic bad. Shadow magic and necromancy (just to name a few) temper the soul by exposing it to processes and energies that most find abhorrent or fear. Purging the fear of death or embracing the shadow self can have very powerful effects on the soul, effectivly transmuting it and tempering it into a stronger force.
Ultimatly they will chose their own paths, and if they have to find some truths out the hard way.. well sometimes thats the only way we're willing to learn. People seeking power eventually find knowledge, and with greater spiritual evolution are we all bettered.