In short, Thrawn doesn't believe to killing unless it's necessary (even mentions it in the book). Even then, he doesn't look at the corpse directly for long.
Okay but Thrawn saying, "If a star whale approaches, destroy it with prejudice," made me laugh so hard. You can almost hear the spite in his voice. I just know he absolutely DESPISES those damn whales for ruining his plans and sending him on a forced sabbatical to a weird ass planet in some godforsaken galaxy with Ezra fucking Bridger as a tag along.
I cannot stress enough to new Star Wars fans that despite the Ahsoka show making him sound like an eldritch magic final boss, Grand Admiral Thrawn is literally just some guy. That's it. Canonically the least Force-sensitive guy in the goddamn universe, with the "Force sensitivity of a rock", employees love him, employers hate him, and his only super power is being the most autistic man ever to destroy environments