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YOU RANG?! 
I’ll take on part of this. And I’m quite comfortable, as I am a non-rapist.
In general, you are taking an Aristotelian approach. Let me say briefly, that Aristotelian logic has been criticized as both lacking the power to “induce” new “truths” and also having a GI/GO factor. “Garbage in, garbage out.”
But let’s focus on the above example.
I would be the first to agree that rape is never justified, and so it would appear that if we are certain that Jack has committed at least one rape, Jack cannot be a moral man.
Or at least, he was not a moral man at the time. What if he was moral until a short time before the rape? (Let’s assume in my analysis that it was a unique action for Jack.) We might well wonder if it would be fair to describe his whole life as not being moral based on the one rape, especially if his prior conduct was not only crime-free, but exemplary.
And, in such an extreme example, I would certainly want to know if there was any evidence that Jack suffered some kind of brain injury, such as a stroke, and his obscenely violent behavior afterward was the result of the resulting change in personality.
This would be an event that Jack certainly didn’t choose, nor would anyone want to. In such an event I could go along with those who generally say that a perpetrator is the first victim of the crime, without wincing or being disgusted.
(This example, BTW, is inspired by an alternate ending to the film “Bubble” in which a woman who truly believes herself innocent of murder finally recalls, in a lock-up, that she alone was standing over the murder victim’s body. And of course she is horrified, despondent and scared to death. But in the alternate ending it is later found that her brain is demonstrably not-quite-right, and she is acquitted.
Just in case anyone was wondering if I was being autobiographical here! :eek: Or talking about another Jack I knew.)
The above isn’t the main point, though. The “no true Scotsman” fallacy specifically refers to the use by some Christians to dismiss any possibility that one can be a Christian, and also a murderer, tyrant or corrupt. etc.
Applying the fallacy-criticism would get into a discussion of born-again versus nominal, and whether, given the distinction, it is common enough or anomalous for the former to act obscenely evil.
This would get into a full-scale religious discussion, which I would certainly not be comfortable with, especially in GQ. 
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(But, BTW, this most common(?) example starts with “No Christian” rather than “No true…” , as others have already alluded to. I was going to be the first to reply; I’ve got to learn to type faster!
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True Blue Jack