Using the instance of Jesus’ good works being attributed to Satan, Denney gets at the basis of why some slander those who do good. While one may take exception to his statement that this is essence of “blaspheme of the Holy Spirit”, he does get at the spiritual and psychology root of much (if not all) slander:

You may think, perhaps, that in this case it is a sin which has very little interest for us—less even than that of speaking a word against the Son of Man. But consider the sin in its nature, as distinct from the particular form in which it was committed by the scribes. They were confronted by the appeal of God’s goodness in Jesus, and rather than yield to it they contrived a hideous explanation of it which should render it impotent both for themselves and others. Is this a sin which is so very uncommon? Or is it not common enough to hear men who are annoyed and reproved by the good deeds of others ascribe these good deeds to base and unworthy motives, so as to relieve the pressure with which they would otherwise bear on their own consciences? This is the essence of the blasphemy against the Holy Spirit. It is the sin of those who find out bad motives for other people’s good actions, so that goodness may be discredited, and its appeal perish, and they themselves and others live on undisturbed by its power. Take one of the most ordinary instances. When a selfish or mean man is confronted by the generosity of another, there is a spontaneous reaction in his moral nature. It is a reaction of admiration. Conscience tells us instinctively that such generosity is good; it is inspired by God; it is worthy of admiration and imitation. But something else in us may speak besides conscience. Perhaps we do not like the man who has done the generous thing; we grudge him the honour and the good will it brings; we would not be sorry to see him discredited a little. Perhaps we are naturally grasping and mean, and our selfish nature resents the reproof of another’s generosity. We should be pleased to think he is no better than he need be. We hint at ostentation and the love of praise; we think of ambition, and of the desire to have a party, which is to be conciliated by such gifts; and the generosity of the man is perverted or ignored. It ceases to be a thing which speaks with power for God to us. This, I repeat, is essentially the sin against the Holy Spirit. It is the sin of finding bad motives for good actions, because the good actions condemn us, and we do not want to yield to their appeal. It is the sin of refusing to acknowledge God when he is manifestly there, and of introducing something Satanic to explain and discredit what has unquestionably God behind it. When this temper is indulged, and has its perfect work, the soul has sunk and hardened into a state in which God appeals to it in vain. The presence of Jesus Himself does not subdue it; it only evokes its virulent, rooted, implacable dislike. This is the sin against the Holy Spirit as it is presented to us in the Gospels.

James Denney, The Way Everlasting: Sermons, “The Deadliness of Slander”  (London; New York; Toronto: Hodder and Stoughton, 1911), 250–252. Thus, slander is an instance of Romans 1:18.