What makes your villain or character kill so easily?

Mainly looking for ideas of this logic and wonder if I got them all? Also like to hear how you execute this or didn’t pay much thought to it.

• actually likes killing and wants excuse
• Too lazy and just kill
• no consequences
• it is the most efficient method
• view themselves as superior status and don’t need to waste time and interact with inferiors.
• Was taught to kill
• Culture as might makes right and fight and death is part of life