It's been said that Epicurean philosophy treats the mind in its healthy, natural state, like positive psychology does, but what happens when people are so sick and broken, psychologically, that they take pleasure in masochism, sadism, and cruelty? What happens when people take pleasure in horrible things.
One reply I can come up with is in PD 39, where we are invited to remove ourselves from the presence of this person, to ostracize a sociopath or psychopath, which our legal and prison system already does. The words used as "so far as it is advantageous, exclude them from your life" - because friendship should be, and is by nature, mutually advantageous. A psychopath provides no advantage by his friendship.
The man who best knows how to meet external threats makes into one family all the creatures he can; and those he can not, he at any rate does not treat as aliens; and where he finds even this impossible, he avoids all dealings, and, so far as is advantageous, excludes them from his life.
If others would like to brainstorms arguments re: psychopaths and pleasure so that we can more accurately debate this issue, please share those here.