Main characters and other positive characters always have healthy sex lives.They might go through long periods of not being in a relationship (they may even be Hollywood Dateless) during which they may have a lot of good sex anyway or not.But when they are in one, the sex is frequent and good (unless the relationship is near its end).A corollary is that when villains have sex, it tends to be quick and emotionless.It will often be treated as an act of self-gratification and only the dominant villain will emerge with their desire sated.When heroes make love, it tends to be caring and passionate, with both parties emerging satisfied.This difference can be cause for a Sex Face Turn for a dissatisfied villain.Of course, this trope applies mainly for experienced adults. In the days before such drugs existed, male impotence was generally perceived as a trait of villains.
In many settings, only characters of questionable morality have "weird" sexual preferences.For really old-fashioned settings, this may even include gays and lesbians.This excludes Very Special Episodes, pleading for tolerance, and series which intentionally include such preferences to be "edgy".Of course, in the latter, most characters have questionable morality anyway.
Note that this idea of "good sex" is sometimes only held by the sympathetic protagonist, who meets humorless people who consider sexual pleasure as depraved and define "good sex" (or "goodsex") by its absence. Compare Ethical Slut and Safe, Sane, and Consensual.
Justified in that one of the primary traits associated with 'good people' is empathy. Contrast Celibate Hero, Sex Is Evil, and Evil Is Sexy.