He leaves no ground for other possibilities. If so, you have proven Mr. Blake wrong. They won't allow a drop of mustard to touch their lips at a potluck while they shovel down four servings . If you think in black and white this is what you do. No possibility of other behavior is allowed.
Irrationality is the only possible result of thinking in terms of good and evil.
This could also be classified as slippery slope thinking. After their children have bolted from the church, and from what they know as a joyless, arbitrary God, extremists often become more extreme, growing increasingly constricted and judgmental, or else carelessly throwing off everything godly for a lifestyle of bitter debauchery . If so, you have shown the fallacy of Mr. Blake's logic. It says that they are bad parents, bad people, and bad Adventists. Also thrown in here for extra effect is hyperbole.