^^^The show may acknowledge that Dexter is not motivated as a vigilante but it is exactly what the show uses to excuse our (supposed) pleasure in Dexter's murders.
This pleasure is why the ever more slipshod plotting of the murders, or the numerous people who somehow have no real problem with his hobby are so acceptable. The whole point is that Dexter is killing bad guys and we are supposed to hurrah.
(In the first seasons, the real charm was in Dexter's private life, as he was a good hearted doofus valiantly trying to cope with his social relationships. And we cared (some of us anyhow) because that good heart conflicted with his Daddy-taught homicidal mania and we wondered what could happen when he finally went sane. All these elements were decisively rejected with Rita's murder.)