My example:
Jo-Jo in the Island of Adventure - i think Jo-Jo should have been kept as a black villain but with the "rolling eyes" and "nigra" speech removed. Changing him to a white man sends the dangerous message to children that a member of a marginalised group cannot be a nasty, small-minded jerk (as TPratchett put it). Women are marginalised but i wouldn't pee on my cruel abrasive mother if she was on fire.