There are many theories as to Human nature. One of
Which exists, under the thoughts of a prominent philosopher, and founder of Psychoanalysis Sigmund Freud.
His deductive argument, entails his conclusion that man is bad, or as Freud explains it as Homo Homini Lupus (man is a wolf to man).
Freud justification for such a drastic approach type conclusion, can by described as basically atrocities of the century Freud lived in. In example the invasion of the Huns, as a brutal entity designed to portray Man's innately evil nature. And the atrocities of the First World War.
Freud's view of Man is an evil one. And that all Men are innately evil and aggression lies within the human as a part of his nature.
Our inclination to aggression is apparent in one's relation with his neighbor and is apparent in everyday casual behavior. Freud also states that as a civilized society we use violence only on criminals and that the law is not able to prosecute the more careful, and smaller aggression of man which can sometimes be just as evil.
Freud also introduces the restrictions set forth by civilization to control the aggressive inclinations of Man (used in the plural sense).
Freud's argument is comprised of factually correct statements ( for his time ). His premises are accepted by many leading Psychologists' today. However the notion that Man is innately evil does not sit well with me and probably not with most optimists, such as myself. His argument's conclusion is well supported and his premises meet the conditions of a deductive argument with relevance and grounds.