Tom Shippey, in one of his very perceptive books on Tolkien's writings, points out that Gandalf would have been a more terrible Ringlord, had he taken the Ring for himself, than almost any other possessor -- including Saruman, Galadriel, and Denethor. For the temptation of the Ring is to fool you into thinking it can enable you to accomplish what you want. And what you want may be Good; but power will make you impatient of the imperfections of those you wish to do Good to.
The Do-gooder, the Reformer, the Theocrat, will end up torturing as assiduously as the cruelest robber baron -- but the robber baron's appetites may some time be sated, his heart occasionally moved to pity for reasons he knows not. But the All-powerful Do-gooder will not let himself rest in his pursuit of "justice," and he will torture his victims with the full approval of his heart. He (or she) is the more to be feared, therefore.
This is the flaw in the Religious Left's justice rhetoric. Yes, we are called to do good. We should even try to influence our society and its government in a positive way. But we must not grasp for power to force others to be good, or to accept the good we think they should have. That way lies the Inquisition.