Guilt by association
This expression is used to refer to judging all members of a certain group to be equally blamed for the behavior, attitude, etc. of a particular member of that group. For example, if a foreigner in Japan behaves in an unacceptable way, that person is viewed with disdain. As result, similar looking foreigners are often viewed with the same disdain. In America where there is much ethnic diversity this is common and also a source of racial discrimination.
Currently all across the United States there are large demonstrations protesting the death of George Floyd at the hands of a white police officer. These protests are aimed at drawing attention to the way police appear to use excessive and unreasonable force when dealing with blacks. A number of video posts showing examples of this would apparently support that supposition.
But while the majority of the demonstrators do protest in a peaceful manner, there are fringe elements that use these demonstrations to vandalize private property and loot. Stores are broken into and their property looted. Often the stores are set on fire. Those are acts of burglary and arson. One thing that stands out when viewing videos of these illegal actions is that the majority of the perpetrators are black. This unfortunately tends to tar all blacks with the same brush. That is to say, there is an assumption made that many blacks are prone to such behavior.
This sort of attitude has led to profiling; in particular, racial profiling. As a result, in America the police tend to deal more harshly with all blacks and certain cases have drawn media attention, such as when a black celebrity is treated in a way by the police that is noticeably different of how they deal with whites in similar situations. This is of course wrong and discriminatory, but one must ask why that happens and the obvious answer is that it comes down to guilt by association.
Returning to the current demonstrations and accompanying violence and illegal acts, it is encouraging to see prominent individuals, such as the brother of George Floyd, condemning such actions and behavior.
I’m afraid the situation in America regarding the current demonstrations is going to get worse before it gets better. There is so much diversity of all types in America, that the radicals in each group tend to fan the flames of hatred which further exacerbates the problem, making reconciliation more difficult and the dangers of escalating violence even greater.
 the act of suspecting or targeting a person on the basis of observed characteristics or behavior