Not a fan of Chuck Riley, but I'm equally not a fan of soundbite "gotcha" politics.
I think it's pretty clear and obvious he was saying that, by the federal legal standards of the time, slavery wasn't considered to be wrong, immoral or unethical. Which is a historically accurate statement as evidenced by the Dred Scott decision.
Trying to turn it into a "Does Chuck Riley support slavery?" soundbite seems a bit petty and disingenuous to me. I'm sure that type of nonsense plays well with certain crowds, but I'm equally sure it doesn't play well with other crowds we need to educate on the salient issue.
And there is an actual issue here, relating to Riley's incorrect (imo) stance on gun background checks. It would be nice if we could take the high road and focus on that instead, and leave the silly histrionics to the hungry-for-histrionics talk radio crowd. IMHO, not taking that approach doesn't do us any favors.