So...good Dr...you've never made an error???
Sometimes, one's worst enemies can become one's strongest allies, once they realize the folly of their ways. It is too early to say with certainty that such a thing has happened to Mr. Zumbo, but it seems likely.
It is important to chastise people who make mistakes enough to ensure that their mistakes are, indeed, mistakes (i.e. that they don't get more benefit from the mistake than they would have gotten from doing the right thing) but punishing people too far beyond that would seem counterproductive.
His apologies and his probable future writings are a net plus on the side of the RKBA, a big plus if that one faux pas article is the sum total of the "damage" done. It's not like he had spent a career trashing RKBA and then did a turnaround. He voiced an assumption of a purist who was sour on the thought of people using improper tools for the craft he loves and as a purist he didn't see any other use for those tools. It was like the thought of someone using a fine skeet gun as an entrenching tool. His problem article brought a ton of education down on him and he did not reject it. He took it in and opened his eyes. That is not to deny that the impending loss of livelihood may have triggered his successful re-education. Paraphrased -the prospect of being hung in the morning concentrates the mind wonderfully from a quote whose author I do not recall.