I've been in a debate here against a number of people who say people claiming to be Christians are actually Christians even when they knowingly go against the clear and plain teachings of Jesus Christ on issues as large as deliberately killing others, lynching others, and so forth.
At one point in the debate, a person named Chris attempted to refute my position (that members of the KKK who were lynching others were not Christians except in name only, which means they were actually not Christians) by claiming that I had been illogical per the "no true Scotsman" fallacy.
Here's my reply:
I don't want to leave the no-true-Scotsman-fallacy fallacy hanging.
Betty is an atheist. If she were to post here that she's a Christian but add that she doesn't believe in God and further believes that the Gospels are entirely a myth (none of it ever happened) and that Jesus never even existed (a position held by many atheists) and you were asked to decide whether or not Betty had converted to Christianity, would you say she had? If you understand true logic, you'd say that of course she had not converted to Christianity. You'd do that because you know that there are logical premises for concluding that one is a Christian and that Betty certainly can be ruled out.
There are differing opinions on the totality of what constitutes Christianity, but an atheist Christian is not a true paradox. If you find this a stretch to make a point, let me tell you that I've run into an "atheist Christian."
So, the so-called no-true-Scotsman fallacy runs right into being itself a false premise.
When one is debating about Christianity, there are arguments made within the context of Christianity and there are arguments that appeal to that there is no God in the first place. Those can overlap or be completely separate matters depending upon the starting place of the debate.
Many people go to the trouble of spelling out things such as by saying, "Assuming that...." It might be said in this thread, "Assuming that Christianity is the belief in God and that Jesus is the son of God who died and was resurrected...."
So, I hope it is clear why Chris was being illogical by invoking the no-true-Scotsman fallacy fallaciously.
Of course, if history is any judge, Chris won't acknowledge such an error or leave off ever misusing the argument again. Which leads to the ad-hominem-fallacy fallacy. In case you're wondering, my point is that Chris isn't trustworthy concerning logic. Chris's premises must always be checked, and it is not a logical fallacy to raise suspicions on account of "the boy who cried wolf." You see, the moral of the story isn't that the adults should always logically be rushing about as if the boy might not be lying for once but rather shame on the boy. The boy wasn't lying simply because he had lied before. The boy was to be suspected of lying at the very least when the wolf had actually shown up, and there is absolutely nothing illogical in a debate by bringing up a history of lying so long as it is not being suggested that the liar is lying because the liar has lied before.
In courts of law, someone who is caught in perjury has his entire testimony stricken and is often cited for perjury, tried, and sentenced. That's how important it is to be wary of illogical people and known liars. The boy who cried wolf shows that its cumulative.
"Ad hominem" is not something to be thrown around lightly, just as "no true Scotsman" isn't.