Ah yes, The Three-Fold Law, Wicca's most overhyped law. First, let me stress to you it is NOT a universal law. If you are not Wiccan, and it does not resonate with you, you do not have to follow it. It is exclusive to the Wiccan religion, and is not a rule of Witchcraft or Paganism. Anyone who forces this law on you as fact, is wrong. It is the same as insisting everyone follows The Ten Commandments when it is only part of the Abrahamic religions.
Now, The Three-Fold Law essentially states ''What you do, good or bad, will return times three.'' This is typically interpreted by newbie Wiccans as ''I push someone, I will get shoved down a flight of stairs, then hit by a car, and struck by lightning.'' Which is complete hogwash. What it actually refers to is how the energy will effect your mind, body and spirit. Doing good deeds brings positive energy and elevates our spiritual vibration, thus improving our body and mind. When we do bad deed, our energetic vibration drops and we feel low. Think about when you feel down, you slouch, your thoughts are sad, and you do not have energy to do much beyond lazing around. Negative energy is heavy and weighs us down. It is not a tick for tack rule. It builds over time.
Most Wiccans do not cast baneful spells because of this and The Rede. (Eight words the Wiccan Rede fulfill: An ye harm none, do what ye will) They work together, but many only follow The Three-Fold Law without The Wiccan Rede. Nothing wrong with that, but you should understand the origin. However, baneful spells are not always bad spells. Some Wiccans are fine with self defense. If someone has wronged you, a justice spell might cause the other person negative consequences, but they are negative consequences from their own actions. Curses can be cleansing. If someone is harassing you, and you are filled with rage, a curse would be you reclaiming your power and fighting back. Whether these instances are right or wrong are subjective. Only you can answer these questions for yourself. This is why you should read the explanation of The Three-Fold Law, then contemplate it. Reflect on how you feel about it. Think about what you feel is morally right or wrong. Question if The Three-Fold Law resonates with you and draw your own conclusions. Do not fear some ''Law'' will strike you down because you did something out of anger. You will learn from your mistakes and do better in future. Nobody is watching you planning your punishments at each misstep. If The Three-Fold Law was anything, it would be the equivalent of someone saying ''Don't go down that road, it's muddy'' and you ignore them. You might get stuck and you will be covered in mud. However, you did not die, you might have lost a shoe, but a quick shower and you know next time to take the other path. That is The Three-Fold Law. Granted, if you believe in it and insist on cursing people for fun over and over, the universe has a way of keeping balance and you might notice your life is not thriving. However, plenty of Witches focus on baneful Magik and live great lives. It comes down to knowing how to work with Magikal energy.