***BRAINZZZ***

Consider the following:

Gramps is quite open about inviting Geralt to his hut and doesn't in the least try to hide his cannibalism. He acts as if he believes he has done nothing wrong (the way a psychopath would act) and seems to take it for granted that Geralt will approve.

When pressed by Geralt, Gramps says he has limits, for example he doesn't eat children. If he only eats dead bodies he finds, wouldn't that be what he would say in his defense?

Also, when asked about dwarf meat, Gramps says he is "ashamed to admit" that he fought off a monster for it, indicating that this is not his usual mode of procurement.

Following the implications, Gramps is at best a human carrion-eater, which is a significant aberration in its own right and indicates at the least a lack of regard for the dead and their loved ones, not to mention a pathological abnormality of the biological appetitive response. So what's to stop the scavenger from developing a taste for fresh meat and becoming a predator? At best he's predator-adjacent, and no internal system of morality that allows one can be relied upon to disallow the other.

If spared, the reward he gives is a formula for a poisonous blade coating.

Perhaps most conclusive, and the closest we can expect to get to the designer's intent, is the fact that the quest XP reward for killing him is greater than that for not killing him.

***BRAINZZZ***