If I follow Steve's accusation correctly, he's saying that Dr. White is inconsistent because:
1) Dr. White distinguishes between "truly religious" Muslims and "nominal" Muslims; but
2) Dr. White criticizes others for saying that ISIS are "true Muslims," because Dr. White states that there is no coherent standard for true Islam.
I can see why Steve might mistakenly believe that these two things are inconsistent with one another. It might sound like Dr. White is saying "you have to distinguish between true Muslims and others," while simultaneously saying, "there is no way of identifying true Muslims."
Unfortunately, Steve has overlooked an important distinction. There's a distinction between nominalism and sincere belief that is distinguishable from the difference between correct and incorrect belief.
By analogy, we see numerous nominal Christians - Christians who identify themselves as such and maybe go through a lot of the motions, but do so for reasons of cultural or personal convenience rather than because they have any actual conviction of the truth.
We also see folks who are in heretical sects (like Roman Catholicism, Mormonism, etc.) that call themselves Christian, but which aren't truly Christian. Even within these sects, we have "true believers" and "nominal" members. Yet those who zealously embrace all of Rome's false doctrines are not "true Christians," even though they are not nominal.
When Dr. White rejects the "all Muslims are terrorists" assertion, he could do so on two different grounds:
1) Nominalism vs. True Believers
2) Multiple Competing Sects of Islam
In other words, John Doe in Riyad may be a Muslim simply because that's what everyone around him is, and if he did something different, he'd get himself into trouble. He doesn't really believe all the stuff they say, and there's no way he's ever going to put his life on the line for Islam.
On the other hand, Jane Doe in Jakarta may be a devout Muslims who sincerely believes the tenets of her particular sect. But if her sect is Ahmadiyya, then she's never going to commit an act of terror, because her beliefs are contrary to such acts.
Both John and Jane are counter-examples to the "all Muslims are terrorists" assertion, but for different reasons. These reasons aren't self-contradictory, they are complementary.
The person who say, "all Muslims are terrorists," has to say both that nominal Muslims aren't really Muslims and also that sects that oppose terrorism aren't really Muslim sects. It's much harder to make a case for the latter point, and that's the point that Dr. White has been primarily addressing.
It's to his credit that TFan attempts to provide a reasonable response. By way of reply:
i) First of all, I can't overlook a distinction which White failed to make. TFan is drawing a distinction that White never made. Assuming it's a valid distinction, that's something that White should have done to clarify his real position.
ii) Keep in mind that I, for one, have never said "all Muslims are terrorists." Although there are people who say that, exclusive focus on disproving that assertion becomes evasive.
iii) In reference to Islam, the distinction between correct and incorrect belief is ambiguous. Since Islam is a false religion, there's a sense in which distinctively Muslim beliefs are false by definition. If truth is the standard of correct belief, then all the competing sects of Islam are objectively false or incorrect (in that sense).
v) There is, though, another standard, and that would be whether a belief is correct or incorrect on grounds internal to the belief system. Although the belief system may be false, if you grant the presuppositions of the belief system, then certain beliefs are consistent (=correct) or inconsistent (=incorrect) in relation to that particular frame of reference.
vi) There is yet another, more relevant consideration. If Muhammad is a role model in Islam, and if the historical Muhammad was a promiscuous, violent man who engaged in military conquest and conversion by the sword, then jihadists are true to Muhammad while liberal Muslims are not.
vii) In addition, the comparison with Christianity simply draws attention to the equivocal analogy. That's the other fork in the dilemma that White boxed himself into. TFan is of course correct that we can distinguish between orthodox Christians and nominal/cultural Christians. That goes to the distinction between orthodoxy and heresy, as well as orthopraxy and heteropraxy.
Problem is, White has said some Muslims have a right to deny that other Muslims are true Muslims. He used the example of the jihadist who gets drunk and has sex with prostitutes. Problem is, the jihadist can still be "truly religious." Can still be "representational of the worshipping community."
He can be sincere. Surely his willingness to die for the cause of Islam is a mark of sincerity, however misguided. That's the antithesis of someone who "doesn't really believe all the stuff they say, and there's no way he's ever going to put his life on the line for Islam."
Likewise, White has admitted that jihadists can rightly justify their position from authoritative texts in Islam. So his jihadist ideology is "correct."
At best, White could try to say that the personal morality of the jihadist (getting drunk, having sex with prostitutes) is a violation of Muslim ethics. But that cuts against the grain of White's claim that there are varieties of sharia, differing interpretations, that it all depends on what traditions a Muslim privileges and his interpretive filter. So it's hard to see anyway to salvage White's argument.
In his latest Dividing Line presentation, he kept using the metaphor of the shoe on the other foot, i.e. what if the situation was reversed, what if the Muslim traded places with the Christian accuser?
Problem is, Muslims and Christians don't wear the same pair of shoes. You can't put a size 7 shoe on a size 11 foot. White keeps attempting an analogy that's vitiated by the disanalogy between Christianity and Islam. The comparison is further nullified by his denial that there's such a thing as true Islam, in contrast to the distinction between orthodoxy and heresy in Christianity.
But I do appreciate TFan's civil, intelligent response–in contrast to White's intemperate, abusive response.