Is it possible for the virtue of justice to be undermined through the acquisition of other vices? St. Thomas Aquinas teaches that the virtues are united--one must have all in order to have any single one. So to have a vice would seem to entail that one cannot have any virtue (or at least to a perfect degree, even at the 'natural' or 'imperfect' level, since all are dependent upon right reason, and vice is the undermining of right reason?).
It also seems to be that the devil works against love of God, and to keep us in the state of mortal sin once we are in it. Does this carry over to the hatred of others? If we lose charity, we cannot have the supernatural love of neighbor. But would the devil also work to destroy any natural love of neighbor that we might have? Should the legislator take into consideration the existence of 'spiritual combat' and its consequences? Or look exclusively at human factors?
If the virtues are one, then it seems that there is some basis for legislating against some "private vices," even if they apparently harm no one else but us. First, we do not belong to ourselves, but to the community, and so I would think that anything that would prevent us from fulfilling our duties towards the community could be prohibited. And secondly, if we can be lead to even greater vices, such as injustice, by having intemperance of some sort, then the ruler would have reason to promote temperance, for the sake of justice. Also, the ruler could prohibit influences or material goods that encourage or facilitate vice. (For example, while solitary sins against chastity by males should not proscribed, since it seems that it is difficult for the majority to avoid them, things that would foster the development of this bad habit [i.e. vice] could be banned.)