This OP is flawed from the get go...
This is quite the popular argument especially with amateur apologists. C.S. Lewis was the first to make it popular and then McDowell reworked it.
I'll quote Jim Perry here on the argument, "It is logically weak, but it is rhetorically powerful..."
It makes the mistake of the informal logical fallacy of false dilemma also called a false dichotomy or in this case a tracheotomy. It involves a
situation in which only two (or three in this case) alternatives are considered, when in fact there are other options. Closely related are failing to
consider a range of options and the tendency to think in extremes, called black-and-white thinking.
From Wiki... "False dilemma can arise intentionally, when fallacy is used in an attempt to force a choice ("If you are not with us, you are against
us.") But the fallacy can arise simply by accidental omission—possibly through a form of wishful thinking or ignorance—rather than by deliberate
deception ("I thought we were friends, but all my friends were at my apartment last night and you weren't there.")
When two alternatives are presented, they are often, though not always, two extreme points on some spectrum of possibilities. This can lend credence
to the larger argument by giving the impression that the options are mutually exclusive, even though they need not be. Furthermore, the options are
typically presented as being collectively exhaustive, in which case the fallacy can be overcome, or at least weakened, by considering other
possibilities, or perhaps by considering a whole spectrum of possibilities, as in fuzzy logic."
The original form of the argument as made by Lewis was ostensibly directed only at refuting the claim, sometimes advanced, that Jesus was a great
moral teacher, but not God. In a nutshell: "If Jesus' claims are not true, then he was either lying about them (which is morally reprehensible) or
he was deluded into believing them, which would make him a raving madman (whom nobody would respect as a teacher); thus he couldn't have been a great
moral teacher." Lewis's version was originally for a radio broadcast, and is probably more properly construed as a rhetorical argument rather than a
formal logical one.
This argument is flawed. First it relies for impact on a premise which is is both ambiguous and controversial, which is the question of just what
"Jesus' claims" were. Second, it makes unwarranted extrapolations from the general idea of saying something known not to be literally true to the
worst sort of malicious lying, and from believing something which is not true to raving lunacy. This second point is dependent upon the first, as the
degree to which one can validly make such extrapolations depends on what the claims in question are, but on a reasonable view they go too far in any
Addressing this argument requires some degree of caution: the basic criticism lies in the fact that none of the three horns of the "trilemma"
actually represent a single possibility, but rather a broad spectrum of possibilities. All that is logically required to refute the trilemma is to
show that the decision "Who is Jesus of Nazareth" cannot be reduced to three and only three clear-cut possibilities.
This basic criticism of the trilemma is echoed by Christian apologist William Lane Craig:
An example of such an unsound argument would be:
1. Jesus was either a liar, a lunatic, or Lord.
2. Jesus was neither a liar nor a lunatic.
3. Therefore, Jesus is Lord.
This is a valid argument inferring one member of a disjunction from the negation of the other members. But the argument is still unsound, because the
first premiss is false: there are other unmentioned alternatives, for example, that Jesus as described in the gospels is a legendary figure, so that
the trilemma is false as it stands.