The problem is that no matter how good your intentions, eventually you want to kill someone yourself.

Hell is paved with good intentions.

Most of the evil in this world is done by people with good intentions.

Your intentions will be good. Without consideration and forethought, however, your actions could still be evil. That is the problem, of course, evil is always easy and resisting it is never so. Evil is relentless; and anyone, if they tire, if they are not vigilant, can fall prey to it.

Half of the results of a good intentions are evil; half the results of an evil intention are good.

But people may do great good accidentally, though with evil intentions - conversely people may do great evil though having the best of intentions.