Which group would have been most likely to criticize the knights of labor?

It would likely be "skilled workers" who would have been most likely to criticize the Knights of Labor, since many skilled laborers and factory owners saw this Union as allowing for unfair bargaining power on behalf of the workers. 

the second significant cause of the great migration was the desire of black southerners to escape segregation, known euphemistically as jim crow. rural african american southerners believed that segregation - and racism and prejudice against blacks - was significantly less intense in the north.

“i think it is very plausible that if there are five votes to end the death penalty, it could be with the people who are on the court right now,” - smith

so basically it is not clearly and consistently imposed