socially and from a populace ethical perspective it is considered wrong. meaning society believes its wrong and so does the popular belief. that makes it ethically wrong

your morals should tell you its wrong because empathy is a basic human instinct. homicidal maniancs lack empathic skills so for them it is acceptable from a moral perspective

from a theological perspective (in terms of god) it is wrong because he commanded man not to. you dont know the potential the individual had and god laid down a rule for you to observe

therefore it is socially, ethically, morally (unless you are a homicidal psychopath) and theologically wrong to murder.

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clicky