Hmm, I never got that impression. Kruge always struck me as being about as nasty and malicious a Klingon as we ever saw.
I agree. Not only was he a renegade, but he also was responsible for the deaths of two crews (Grissom
and the merchant vessel), a Federation scientist, and (indirectly) the destruction of one of Starfleet's most celebrated vessels. And he did all of this in the name of acquiring further knowledge of the Genesis experiment, even as his government gradually worked toward peace with the UFP.
As an aside, I always laughed the Klingon Ambassador's claims that Kirk should have been extradited following Kruge's death and the theft of the BOP. Kruge took his
ship and crew into Federation space- to a sector that even Starfleet officers were forbidden to enter without permission- and carried out each of the actions I've listed above.
The Ambassador comes off as a bully in his exchange with Sarek and President Roth. He argues that the Klingons have the right to preserve their race but then whines about Kirk standing for himself and his crew. What did he think was going to happen after Kruge killed Kirk's son? Granted, Kruge didn't realize what he'd done until a grief-stricken Kirk shouted at him and called him names, but he shouldn't have ordered David's death in the first place, nor should he have taken two Starfleet officers as additional hostages. Kirk was absolutely justified in taking action to protect his crew and preventing the Enterprise
from being captured by the Klingons.