Dark Magick is just that.

Dark or black magick is just that, no matter what name you want to try and white wash or justify it with. You, and only you, will pay the price even if you pay someone else to do it.
Let's talk about what constitutes the Dark Arts. They are not defined as for personal gain but as attempting to force someone to do something against their will or against their best interests or harming another or working against the greater good. The last will get you the least smut on your soul as most of us are not capable of seeing that far into the future.
Let me give you an example of some very black working all prettied up in the" for your own good" category and the "we really didn't know what we were doing so we really, really screwed someone up good" secondary category.
Trust me, the payback is always bad. Ignorance is no excuse.

A gentleman came to me because he was having a spate of "bad luck" that was driving him to financial ruin and his friend, whom I had counseled, recommended me. He really didn't understand how exactly these nice "church ladies" could be "cursing" him. However, since my friend had almost lost his life to the workings of a similar group he knew what he was seeing.

Unlike the "wizard for hire" bunch, I question my potential clients carefully and I have the training to get answers. I was totally puzzled. The problem was simply that the mother did not want her daughter involved with him. Okay, here is a man who owns his own business, car and home, is financially solvent and good looking to boot. I could have five women fighting over him with a phone call. So, I bluntly asked exactly what was wrong with him. He replied, "I'm a Presbyterian." That caused uncontrollable head shaking and eye blinking on my part. "WHAT?????"
Then I asked exactly what these women were doing to him and how this "mother" convinced them to do it and by the way, who are they? It turns out the "they" was a prayer circle in a little Fundamentalist Church. "They" were meeting twice a week to "pray" that he be stopped from dating her daughter and that her daughter quit working for him.

Now, let me explain quickly why this IS the DARK ARTS. There is no difference between praying, chanting and standing on your head imagining or casting a well crafted circle,  lighting incense and invoking your chosen God/desses. The problem with this group is they were totally uneducated in the arts they were invoking. By leaving the prayer open ended (he be stopped from dating her daughter) they left the door wide open for any entity listening to use any means (including killing this man) to do the job. Without a circle of protection, they had left an open door for anything and anything always has a price. They left an equally open door on the daughter quiting the job and as a result, he was suffering a myriad of health problems (and this was a healthy guy) preventing him from "dating" and his business was going under hence the daughter not working  for him would be because there would be no business. This would hurt not only him, but the community his business serviced.

I asked how he got into this mess and his reply was the daughter rebelling against the restrictive faith of the mother had picked him out for her little rebellion and since she was pretty and a good sales person, at the time he didn't see any harm. He really didn't want to date her in the first place but she chased him. She had spent a week convincing him to hire her on a commission basis with the old "what have you got to lose" argument. He was quickly finding out what he had to lose.

So, I taught him cleansing and basic protection magick, none of which conflicted with his religion. In the end, he had to sell the business to get rid of this mother/daughter team from Hades as when he tried to fire her, she went to the prayer circle with a list of grievances and they then redoubled their efforts to now "punish him". That was when they really stepped over the line into the Dark Arts and I have no doubt paid the price.

So, what happens when you step over the line?
It is all energy and energy is neutral. It is all how you use it. When you attempt to go against another's best interests or desires, you have to use more energy than just going with the flow. One person can only channel so much energy so unless you are very skilled "vampire" you are going to weaken. First your aura goes and eventually your body follows but your mind is going to go before that happens. Without your aura to shield your mind, and severely weakened, you are prey for every creature of the other realms who wants a snack of your energy and sanity. There are plenty of them.
A group of people can raise more energy than the individual members taken singularly. One thing every High Priestess knows is that channeling the energy of a group is like walking a moving tight rope that was greased. That's why you don't get the head piece by passing a written test. Even with a well organized group, one person out of it that night can cause the energy circle to tilt and if the circle breaks, the energy feedback is, well, Hell. Headaches, nausea, weakness and dizziness are the weaker of the symptoms of a circle gone bad and that includes a prayer circle. There may be a temporary "high" and then the symptoms hit anywhere from an hour to a day later. I have seen people literally thrown to the ground and bounced off walls. The problem in prayer circles is simple. How well do you know the people you are working with? Everyone is nicely praying for poor Mable's recovery when one person suddenly thinks, oh, and could you get rid of my daughter's fiancee. Suddenly, your healing circle dipped into the Black Arts and poor Mabel is going to pay right along with you. Someone always pays.
With a good High Priestess, we know the moment the energy moves to a new level and will stop it. Our members also know the danger if the circle unbalances before the energy is released and aren't gong to play add a little prayer to it. We work in a purified and sealed environment. Hey, there is a reason the Pope is swinging that censor and chanting in Latin around the altar and those priests and choir boys and going up and down the aisles and around the perimeter of the Church at all major services. Too bad your pastor can't speak Latin and doesn't know why. The local witch knows why. He's not going to take the chance that the local JC impostor shows up to Mass. He's making sure he gets the clear, unfettered and open line to the real thing.
What happens if you persist on this path aside from insanity, rocking back and forth in a padded cell while watching the local entities eat you? You mean that didn't scare the crap out of you? Well, you get to die a long and lingering death because you aren't as valuable in their world as ours. Here you are food. Once you cross over, all the things you did arrive to haunt you and unfortunately for you they will be really, really real. You will find you are virtually a slave in the afterlife to whoever or whatever is stronger than you and there will be someone stronger than you waiting for you. I have been told the pain is excruciating because your soul is not intact and you feel like you are constantly hungry and  thirsty trying to replenish it. Shall I go on or are you getting the idea that anyone who tries to rope you into these things is no friend of anyone but themselves.
The bottom line is you wouldn't play with explosives with a group of people smoking and who have no knowledge of safety precautions. Don't play with energy the same way.