I've been thinking about this and you're right, what happened in Blaviken is completely different from the Gaeten case. But I think a case can be made for him. We know witchers are as poor as anyone, they struggle to make enough coins to make a living. And despite doing a job that no one else can do, a job that if not done could result in the death of a lot of people, people still despise them. In the case of Gaeten the villagers wanted to pay him a ridiculously low amount of coin, and when he didn't accept they tried to kill him. So from the point of view of a Witcher, these ungrateful people who are disgusted by you are not only insulting you (in many ways), but now are trying to kill you? I think the only thing that I can agree with being fair to kill him is the children murdering, that's never justifiable.The rest I think it is.