Over on Fern's Fronds, Fern Bernstein-Miller has a fantastic post on the "Threefold Law of Returns." You need to check this out. Especially if you're thinking "isn't that the rule that says everything you do comes back to you threefold?" Because, well, it's not. And while Fern has much more to say on the topic, perhaps the most salient point she makes is this: "[The Threefold Law] means that you are expected to take an active, involved role in creating Justice right here on Earth."
It should be pointedly obvious to anyone with a double-digit IQ that evil is not always punished threefold -- hell, often it's not even punished at all. There are plenty of thoroughly nasty people who get rewarded for their nastiness: the rise and continuing rise of Goldman Sachs would be one good case in point. And good behavior doesn't always result in benefits. Sometimes it even results in martyrdom. It could be said that these Goldman bigwigs and slaughtered Syrian dissidents will all get what they have coming in a future life. But that's rather a large leap of faith, and one that can bring us to some truly noxious conclusions. Is every victim of gang rape or repeated sexual abuse working off karma for a past life as a rapist? Are birth defects a punishment for misdeeds in your last incarnation? What kind of crimes warrant childhood cancer? Is inherited wealth a sign of higher spiritual evolution, while birth into poverty is a sign of corresponding spiritual inferiority?
A morality which runs on "I do good things because I get rewarded for them, and avoid doing bad things in fear of punishment" is hardly a great achievement. It's easy enough to train flatworms by means of reward and punishment. The trick is getting people to do moral things when it would be easier and more profitable to break the rules, or to avoid the issue altogether. And while the common interpretation of the "Threefold Law" may work at stopping sins of commission - at least as well as the "you'll burn in hell if Jesus catches you masturbating" line works, anyway - it's horribly likely to encourage sins of omission. Why bother engaging with evil if karma (or the Western misunderstanding of karma) is going to take care of the issue for you? I much prefer Orion Foxwood's concept of "co-creators." We are spiritual beings walking a human path: we have incarnated not only to avoid evil but to do good. And when we shirk that duty - when we avoid calling out injustice and tolerate unrighteousness - we have failed in our mission. That places a tremendous burden of responsibility on our shoulders.
Following the prohibition "you should never do magic to harm another" is relatively easy. What about "you should use magic - and any other tool in your kit - against those who willfully and wantonly harm others?" That is far more difficult. It requires a great deal of thought and careful consideration. It leaves you open to making a wrong choice and hurting those who need healing, or to taking the wrong side in a fight. It forces you to choose your battles carefully, and to understand and accept the possible consequences. But nobody ever said magical traditions - or ethical questions - were easy. Sometimes a morally ambiguous world demands a morally ambiguous response: there are times when inaction is no longer a tenable option.