Is this some sort of attempt to use presuppositional apologetics to hand-wave away the high numbers of Christian criminals?You are misapplying the NTS fallacy.
For the NTS fallacy to exist, "no true" something, something true must first exist along with the definitions of what is "false" and what is "true". The NTS fallacy includes the axiom:
True things exist and false things exist.
These are called by we Christians absolutes, and are used to demonstrate that immaterial absolutes (truth, falsity, God, spirit, math, logic, love, justice et al) exist. Thus I encourage atheists never to invoke the NTS fallacy, for it is based on axiomatic truths that immaterial realities exist.
Here's the thing about the "no true Scotsman" fallacy: pointing it out isn't an appeal to some sort of absolute truth; it's calling attention to hypocrisy. The definition of Scotsman is merely agreed upon; it isn't defined by any sort of universal truth. The issue is that the person committing the fallacy is hypocritically assuming a new definition for the purposes of the immediate argument that contradicts either the definition he still holds or the commonly held definition - i.e. what he could reasonably expect other people to understand by the term when he says "Scotsman".
Jesus's assumed opinion on who he would save or who he approves of is irrelevant. That isn't how the definition of "Christian" is used in this society: we don't make assumptions about whether a denomination's doctrines are true when deciding whether they're "Christian" or not.Further, since Jesus Christ said "you must be born again to be a Christian and follow me," I should think that HE is entitled to say some true Christians exist, and what determines them to exist, i.e. being truly born again. After all, atheists LOVE to say Jesus was the first one to espouse Christianity but the NT writers messed it up.