I would personally like to say that yes it exists and it has effects on people, however, as we all know, what goes around comes around. The power of magic that backfires is far worse than the first fire shot at someone else. A person has all the capabilities of getting over it as much as it might harm in the present, but once it does so, it helps the individual and digs a hole for the attacker. Similarly, such doings attract negative forces and in all honesty, you as an attacker will affect the people around yourself, slowly driving yourself to exclusion and madness ^^ And here I got out of the empath sphere only.
These people feel "burned" when "scanned" or talked to about such things, and nevertheless have to deal with blockages and other bs. Imo, I'd just mind my own business and let the law of attraction and karma do their job for revenge and grudge channeled in the ways of 'black magic' suggest a big imbalance, and from here we can move forward to talking about love and how many problems it can solve when delivered at the right time.
Just a quick insight but everything is fixable and responds to higher frequencies. And why not, to lower ones as well *cough*
There's that nice concept of the Japanese people, the art of repairing a broken piece of pottery so that it ends up looking more beautiful than before: Kintsugi.