Nobody at this point has enough information about the actual circumstances to know whether it would be justified to feel "anger at 1000 people standing by". What we have been told is that some of those people risked their lives trying to stop it, in face of gunfire, and one was killed.

It is very easy for anger at atrocities carried out by people belonging to or even acting ostensibly in the name of some religion or nation (or whatever), to be used as a way of generating hate against members of that religion or nation (or whatever). And the outcome often enough has been horrible - riots, lynchings, pogroms...

It is not right to attack people who try to prevent this process as if they were somehow defending the people who were responsible for the original atrocity.