Because they can't call them black mobs.
They could be called "blobs."
The context of the usage would indicate the nature of the reference.
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The first of these things to get publicity were “cultural events” with theater and choral troupes assembling to stage a dance scene or sing the Hallelujah Chorus. The possibilities of the technique, of course rapidly spread to less savory participants and intentions. Now we have the black gangs in Peoria seeming to be intent o making the city unlivable for non members. This crap is spreading rapidly and may be the thing that finally induces me to get a carry permit. I have avoided that to date because I don’t want my name on the first list the government will use when/if they decide to confiscate.
BINGO!!