What really WAS the point of Lep's intrusion? (Possible Spoilers!!)

POSSIBLE SPOILERS!!
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I've now watched this two or three times and maybe I am missing something but one thing keeps getting to me, which is the scene where Harry asks sort of rhetorically, what do they want, or what is the point of the intrusion and related events? Were they really just a bunch of psychopathic animals who were fixated on raping and killing the two, or was there some kind of plan? What did Lep and the boys actually hope to gain by doing what they were doing? Or were they just punks who simply lived to smash up nice stuff as a way of getting back at the world? And if so, getting back at the world for what?

One thing I did get out of it is a sort of twisted DEATH WISH in reverse, where the punks take the action to the person who will eliminate them rather than forcing that person to go out and find them. I almost think that Lep knew that he would not survive the encounter, deliberately letting himself be killed to fulfill some twisted need within himself to be bested by Vaccaro. The moment where he takes the shotgun and tells Harry to run for it seems to be the turning point in the film: Everything that happened before it goes flying out the window and the only thing that matters is seeing the event through to it's logical conclusion, which would have been the thugs each having a go at Vaccaro and then snuffing her.

But again, to what gain? Unless it's just psychopatic insanity, what were they hoping to get out of the effort?