The black actors were filling in for the white radio actors and had to deliberately imitate the voices from the show, and Tim Moore as the Kingfish, although a great comic actor, might've been overdoing it a tad. (When you hear a parody of offensive black stereotypes going "Ohh, holy mac-kerel, dere", that's Moore's signature delivery.) By the 60's, everyone had forgotten about the radio show, and was getting on their high horses about the roles blacks were "forced" to play on TV, and the reruns had been on so annoyingly long, it made too easy a scapegoat. But apart from whatever it brought from 40's radio, there's almost nothing offensive in it--We even see other mainstream professional black policemen, judges, secretaries, etc. in the stories; like Ralph & Ed, it's only our heroes that aren't the sharpest tools in the shed.