That's not a normal or civilized manner of responding to a heckler.
On a scale of things to worry about, Michael Richards' attitudes towards minorities might be low on the list, but it is discouraging to see someone with all the advantages and benefits he has had do something like this, and set people against each other. Rickles' humor was borderline edgy, but you knew what his schtick was when you went to see him. He made watermelon and fried chicken jokes, which were funny in the 60s as America was working things out on race, but which have gotten a little old and stale. But he certainly didn't suggest that the good old days were when blacks could be lynched--"stick a fork in him upside down" was how Richards put it. That doesn't magically jump out of someone's mouth, it was already in his head.
Richards has shown himself to be very pettty and hateful. Of course there is a double standard but that does not mean there shouldn't be standards. I admit I got petty enjoyment from how Richards looked around with dismay as the audience walked out on him.