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People who are prone to aggressive behavior can become dangerous individuals.
Literal
Aggressive-[attributive-な] behavior [to-に] prone people [topic-は], dangerous-[attributive-な] human [to-に]-become-can-[potential-え].
Psychology/social commentary. ~に出やすい ('prone to doing X, tends to X') combines に with 出る ('go out, show up') + ~やすい ('easy to'). なり得る is the potential form of なる ('become') + 得る ('be possible') — 'can become, is possible to become.' 得る read える or うる is a formal auxiliary for potentiality, often attached to verb stems — ありえる ('is possible'), なりえる ('can become'), 考えられる ('can be thought').