Ethics of Witchcraft
It's the responsibility of the witch to determine her/his personal code of ethics when it comes to magick. It's generally accepted in Wiccan circles that performing any sort of magick to influence someone is wrong. Each person should be able to have free will, using magick to influence free will is usually frowned on.
Then there's gray areas such as performing healing spells for someone who is sick without their permission. Some hold to the idea that no spell should be cast on or for another person without their permission. Yet others would say that because it harms none and is meant to do good that it is fine. This is something the caster must comes to terms with.
Another ethical dilemma is the area of love spells. In my experience, love spells are one of the most popular spells people seek out. The problem arises with the caster deliberately trying to influence the emotions of their target. The spell could work in several ways... expanding a love already there, creating a false sense of love for the caster etc. The problem with this, is that it becomes a synthetic feeling, not natural. I would say it's the equivalent of giving someone a date rape drug but on the emotional/spiritual level. The target's free will is disregarded so the caster can get what they want... emotional fulfillment (as opposed to physical gratification such as a date rape drug gives). In the end it's your path and you get to choose which road you go down.
Most witches believe in Karma/The Law of Three (what you do comes back to you three fold)/The Golden Rule. Basically, you reap what you so. So if you curse others, by the law of three it will come back to you three times as worse. It's always best to do unto others what you want them to do to you. Remember, there are always consequences for your actions and eventually you will have to answer for any ill you do to others. The bright side is, you'll eventually reap rewards for the good you do as well.
Whenever you're in doubt or on the fence about something I suggest you consult your spirit guide. It's there to guide and protect you while you learn your lessons in this life.