Natural Virtues and Vices

Hume identifies a distinction between natural and artifical virtues and vices but the two are more closely tied than their titles would suggest. Artificial virtues are virtues that are "made" by society in order to benefit it. An artificial virtue may be something like "political justice" or "politeness" which are agreed upon by everyone to be beneficial but which must appeal to a natural virtue in order to be legitimate. A natural virtue is something like sympathy which does not have to be reasoned (at least according to Hume) and is simply felt. For example a politician may make an overture for the artificial virtue of political justice but it is our natural virtue of sympathy that lends this plea weight.
Here sympathy does not seem to mean the same thing as compassion, which is a sort of limitless forgiveness for circumstance, but rather acts as a sort of universal law based on humanities similiar dispositions. Because we all have relatively universal feelings (pain, pleasure, ect) we can identify in someone qualities that we esteem (or despise) in ourselves or qualities that we wish we had (or are glad that we don't). Sympathy then, "is the source of the esteem, which we pay to all the artificial virtues." (369). Hume draws finer and finer distinctions throughout the chapter (ex: we are more likely to sympathsize with someone who is relatively closer or better known to us) but the same general principle runs throughout. The question I would pose here is how this accounts for people like sociopaths who perhaps take advantage of people's sympathy without feeling any of their own.
Also, I don't even know where to begin on this quote but it seems from the paragraph following it that it deals with proximity in regards to the level of sympathy felt (ex: more sympathetic to shipwrecked sailors if I can see them then if I simply read about them).
"In all kinds of comparison an object makes us always receive from another, to which it is compared, a sensation contrary to what arises from itself in its direct and immediate survey. The direct survey of another's pleasure naturally gives us pleasure, and therefore produces pain when compared with our own. His pain considered in itself, is painful to us, but augments the idea of our own happiness, and gives us pleasure." (emphasis mine).
Hume seems to be saying that through the natural virtue of sympathy we will feel happy when someone around us is happy but this pleasure raises our expectations and will produce more pain in us (and vice versa for someone expiriencing pain in proximity to us- we will eventually derive pleasure). This seems to say that someone emoting near us will produce both pleasure and pain. If this is the case how can we say something is moral in Hume's system? Something is moral, according to Hume, if it illicits a feeling of pleasure in us, but if nearly all things will illicit both pleasure and pain then is anything properly moral in a Humean sense?