the possibility does exist that Husnock culture was strongly biased towards that sort of xenophobic ultraviolence. Hints of this can be found not only in what the Husnock did to the planet but in what Kevin said about how his efforts to use his powers of illusion to keep the Husnock off only made them angrier and crueller.
Exactly. And unlike those examples
Sci gave, the Husnock are a strictly fictional species - they are
only what the writers make them. Hypothetically, the Husnock really CAN be exactly what Kevin Uxbridge said they were. And why should that be dismissed out of hand? Because it's not "realistic"? This is bloody *sci-fi* we're talking about here - that ship sailed a long time ago.
There is a thing called "verisimilitude." To simplify the concept, it generally means "plausibility within the constraints of the genre being depicted."
It is not plausible, within the conceits of the
Star Trek Universe, to infer that the general nature of a species of seven billion individuals is represented by the actions of a single known starship crew.
There have, in fact, been numerous examples of starship crews in the
Star Trek Universe whose behavior deviates from the norm for their species. The Ferengi encountered in "The Last Outpost" were much more violent and hostile than most Ferengi, for instance. The Federation crew of the
U.S.S. Equinox certainly weren't representative of what most Federates are like. The crew of the
I.K.S. Rotarran were nothing like most Klingon crews before Worf and Martok whipped them into shape. Etc., etc., etc.
So the idea that it's reasonable, within the rules of the
Star Trek Universe, to infer what the Husnock are like based on one ship's behavior is, again, just absurd.
As for a single starship crew: Is there any evidence that a single Husnock vessel was responsible for what happened at this colony? That's all that Kevin "sent" against the Enterprise, but is that all that the real Husnock sent to destroy the planet? For all we know, the Husnock sent a fleet to attack.
Seems odd that he wouldn't have "sent" a bigger fleet if he'd encountered a bigger fleet. And the STU is full of examples of fleets that behave in ways that deviate from what their peoples are usually like, too; the Vulcan fleet attempting to invade Andoria, for instance.