I would argue that harems are, in principle, self-serving and not selfish. This may sound like the same shit, but I believe that just because one will form a harem just to get off, it does not mean it needs to be ONLY about that one person. Hence why I categorize the harem between selfish and not.
Harems, by proxy, vary in type and how they are formed. Generally the ideal is conqueror mind set of having a number of partners that you can satisfy ones lusts. Yet, there are some harems that are built on the grounds of true affection and love with intimacy being some measure of an after thought.
In AVN terms, the term harem is simple: Have all the hottest chicks love/lust after the MC, with some measure of drama/jealousy/problems have now and then. Here, founding a harem would depend on who all is involved and how it's really approached. And naturally, which route is at play.