There are two main motivational systems right? Approach vs avoidance. Introverts tend to be heavy on the avoidance side and extroverts on the approach, and I notice on this forum people tend to posit avoidance/fear as the "real motivation" for most behaviour. But regardless, both systems exist in everyone, and for most acts one's motivation may come from either system. Killing is no different imo - it can be an act of joy/desire (approach-based). It's probably not for the majority of people (and comes from fear/the avoidance system, as you said), but for a special few it would be.
Malice more generally I'm not sure about, but I think it quite possible that again, either motivational system can produce it. Fear/avoidance, for the reasons you said, and desire/approach, because of sadism/thrilling in causing harm.
(I *have* often found fear to be the root motivation behind a lot of negative behaviour though.)