You're right.   But if a person is already in a defensive posture, say they know they are in a domestic dispute, they are 'accutely' aware of the possibility of violence, even if they have never met the people there are dealing with.   Past history/experiences affect ALL of us and many of us develop fears that exceed the threat.   I had an aunt, very nice lady, who would be near tears every time she went on a bridge over water.     
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In St. Louis circa 1976 I talked to city police.  They would drive 60 through the projects I was staying in (with permission from black gangs).   Why, it's it terrible police work?   They were never out of their car unless in pursuit.   Why?, because they got shot at from high points in the apartments.  One guy had his police car striped when he chased a subject to a fourth floor apartment.   

So yes, a defensive posture is logical.   It also creates a stereotype, based on skin color, that could trigger fear and cost a harmless person their life.