Instead of hoping to resolve differences peacefully, they go out of their way to find conflict. The carnage that then ensues impacts more than just the intended target. However, since they're so bloodthirsty in the first place, these characters don't care about the consequences of their dispositions.
Attack On Titan's Eren Yeager is responsible for one of the most notorious atrocities in all of anime. By using the Founding Titan to invoke the Rumbling, he butchered 80% of the global population in a matter of days.
This renders him one of the most heinous war criminals in anime, especially since his body count numbers in the billions. Eren justifies his actions with the notion that the outside world would have done the same to Paradis. Many years in the future, the Rumbling's vengeful survivors proved him right by destroying his home island.