This thing about how if you try to harm someone and then it will come back to you 3 times as worse is really not true. All magic is neutral because everything you do has "good" and "bad" consequences. So if this rule where you get punished for harming someone was true, then you'd be punished every time you use magic.
For example, if you use magic to get a job then the good outcome is that you get a job. However the bad outcome is someone else who really needed that job was turned down.
This rule has been made in every religion as a way into manipulating people to do the "right" thing. If you want to go ahead and believe it that is fine, but don't go around telling everyone that something bad is going to happen to them.