A thing that annoys me is people who try to force total moral ambiguity into a setting where it doesn't make sense.
Such as a setting where "good" and "evil" are literal, tangible forces that can fuel magic and where For The Evulz is actually practical.
Yes, that spell will make you evil, because it is fueled by evil energies.
No, Paladin, you cannot just graciously accept Infernal Healing, it's fueled with evil energy and was created by Asmodeus, who is most likely an enemy of whatever deity you worship.
No, Good Cleric, you cannot cast the spell, your god doesn't grant that power because she is a good god and it is an evil power.