The humans can think rationally, and this very ability of thinking, can, and in most cases does, prompt them in the dark domain of 'irrationality', and if proper wisdom and judgement are not utilized, then they are driven to 'irrational' acts; and if these humans do not do any self analysis, and if they are not warned by the other wiser people, then they would think, what they are doing or have done is/was right; even though the majority of the other people would think that such acts were wrong and against the principle of kindness and love.
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