With virtues and sins, there is often a point of similarity between them that seems to cause some people to get confused, and even to think that they are not really much different from each other.
As an example, image that there are two men who know the same woman. One man loves her as truly as he able, cares for her and wants to see her happy. He tries to help and protect, and would give his life for hers should the need arise.
The other man sees her as an object of desire, and wants only to consume her on his own lusts. Perhaps he will treat her kindly, but it is all calculated to his own ends.
On a superficial level, one could say that if either man had his way, the results would be the same--whether through marriage or not (and there's no reason to think that the second man would not marry her, especially if he regarded it as 'only a ceremony') each would have a sexual encounter with her.
And the same could be said of other virtue/vice pairs. In both justice and revenge, there is the desire for the punishing of the guilty, and even to the point of ending the guilty person's life should the crime be so heinous. Chesterton in 'Orthodoxy' points out that some in his time tried to say that the martyr and the suicide were actually the same, because both choose death. Peace and cowardice are too often mistaken for each other, because both do not want conflict.
But they are not the same, despite the one point of superficial similarity they may have. Love and lust are not the same, and saying that each would lead to sex is not saying they are the same. For the man who loves a woman, she will be much more then just a sexual partner, much more then just a body. She will be a person, and he will care for the whole of her. For the man with lust only, she will be only an object, a thing by which he pleases himself.
And it is here that the true difference comes out. It was C.S. Lewis who noted that the modern virtue has become 'unselfishness', while the old virtue was 'love'. The difference was subtle but important--'unselfishness' is actually a selfish 'virtue', because the important aspect is the doing without, while 'love' has the wants and needs of the one loved as its main consideration.
For the man in love, the woman, the beloved, is his concern. For the man in lust, his own desires are his main concern. For those wanting justice, the law and it's consequence are what is important, while to those wanting revenge the main thing is their own 'blood lust'. The martyr dies for things higher then himself or herself, while the suicide dies only for his or her own self. Those who love peace will see the need to fight for it at times, while cowards will have no conflict but also no peace.
And perhaps that should be expected. Evil may be likened to a parasite, or a leech. It can only exist because it has a good think to take life from. Evil may also been seen as the deformation of a good thing. If such is the case, the point of connection between the good and the evil would be similar, but that would not make the them the same things--if anything, it makes the evil more evil, because it must lessen the good and take life from it in order to exist.