Don McLeroy is a dentist in suburban Texas with the geeky, earnest manner of an American guy who has educated himself, however imperfectly, on a wide variety of topics. With his balding pate and high-waisted, pleated slacks, he makes Ned Flanders from “The Simpsons” look like Mick Jagger, circa 1969. I found myself utterly unable to resist McLeroy, who is likable and 100 percent sincere. He’d be a great neighbor, in large ways and small; the kind of guy who’d pull over on a busy highway to help a stranded motorist, while everybody else zoomed past. But as we see in the documentary “The Revisionaries,” it’d be a mistake to consider him harmless just because he’s a nice fellow.