Kundi
I can't tell you how to work out these logical inconsistencies. I can only put forward how I attempt to make sense of them. My solution, after years of looking at Adversus Marcionem is as follows:
1. acknowledge that there are layers to the existing text. What I mean is that - along with Andrew Criddle - you have to recognize that the deepest layer of the text has nothing to do with Luke. It was written by Justin or someone in his circle about a 'super gospel' (= harmony) and (perhaps) the similarities and differences with the Marcionite text (but this also might have been added later). It has nothing to do with Luke only insofar as a later editor (probably Irenaeus) assimilated and reordered the original 'super gospel' commentary.
2. pay careful attention to what is actually said in the text. I have come to the conclusion that in many places we see signs that Luke's modeling was influenced by the original Adversus Marcionem text rather than the other way around. Take what is said right in the first sentence:
Christ knew "the baptism of John, whence it was." Then why did He ask them, as if He knew not? He knew that the Pharisees would not give Him an answer; then why did He ask in vain? Was it that He might judge them out of their own mouth, or their own heart? Suppose you refer these points to an excuse of the Creator, or to His comparison with Christ; then consider what would have happened if the Pharisees had replied to His question. Suppose their answer to have been, that John's baptism was "of men," they would have been immediately stoned to death.
Let's take it line by line. But before we do let's note one thing that comes from a related discussion in Irenaeus:
Moreover, by His not replying to those who said to Him, "By what power doest Thou this?" but by a question on His own side, put them to utter confusion; by His thus not replying, according to their interpretation, He showed the unutterable nature of the Father. [Adv Haer 20:1.1]
Clearly the end game of the discussion is the heretical contention that the Jews didn't know know the ultimate god only an angel. This is important because it provides us with some context for what appears in the other text. In other words:
a) Jesus did not reply to the question directly (= because of a secret power in heaven)
b) his response put them to confusion
Now back to Adversus Marcionem. It begins with an assertion:
Christ knew "the baptism of John, whence it was."
A citation of the gospel. Good start to accepting that the ur-text referenced and knew the gospel. Next:
Then why did He ask them, as if He knew not?
So the next statement compares the fact that both Jesus and the Pharisees ask questions as a means of diffusing the claim of the Marcionites that the Jews were ignorant of the Father. In other words, it wasn't as if the gospel writer was trying to show that the Jews only knew an angelic power not the ultimate god.
I think the line that follows show that the original text was written before Matthew or Luke. We read:
He knew that the Pharisees would not give Him an answer; then why did He ask in vain? Was it that He might judge them out of their own mouth, or their own heart?
I think the original text that appeared in the account of both the Marcionites and the super gospel of Justin more closely resembled what appears in Mark now:
27 They arrived again in Jerusalem, and while Jesus was walking in the temple courts, the chief priests, the teachers of the law and the elders came to him. 28 “By what authority are you doing these things?” they asked. “And who gave you authority to do this?”
29 Jesus replied, “I will ask you one question. Answer me, and I will tell you by what authority I am doing these things. 30 John’s baptism—was it from heaven, or of human origin? Tell me!”
31 They discussed it among themselves and said, “If we say, ‘From heaven,’ he will ask, ‘Then why didn’t you believe him?’ 32 But if we say, ‘Of human origin’ …” (They feared the people, for everyone held that John really was a prophet.)
33 So they answered Jesus, “We don’t know.”
Jesus said, “Neither will I tell you by what authority I am doing these things.”
The only difference is that I think all the deliberation narrated as going on in the heads of the Pharisees wasn't there. Moreover if you read Tertullian the implication is clearly that the Pharisees didn't answer at all. I think the Pharisees being silent about the baptism of John is important.
Moreover if you read Tertullian's De Baptismo chapter 10 you will see an important distinction from our inherited assumptions. Here the idea is spelled out that it wasn't just that the Pharisees 'believed' that the baptism of John was 'of men' (i.e. an opinion of the Jews) but rather a 'fact' agreed upon by the author of the gospel (presumably) and the Pharisees. In other words, 'Tertullian' (or whomever wrote the original treatise) puts forward the idea that it is obvious that John's baptism was not from heaven. This a mutually agreed upon 'fact.' To this end, we must reconsider what the silence of the Pharisees really means. Were they silent because they knew that it only established the proselytes as 'Jews' according to men (a Pauline theme i.e. juxtaposing the 'inner Jews' from 'outer' ones)? I think this is the original meaning.
In other words, it is only with the addition of the 'inner dialogue' narrative which was added to the ur-gospel that we get distracted from contradiction which Origen brings up in Commentary on John 10. The entire relationship between the Pharisees and the baptism of John in the gospel is hopelessly contradictory. At one instant they too undergo the baptism (Matthew). But if this is true, why does Jesus say in another part of Matthew that they think John 'has a devil.'
IMHO the whole mess becomes more understandable if we imagine the 'baptism of John' went back to the massive conversion of all the neighboring tribes of Judea (we may even extend this to the activities of John Hyrcanus's sons). In other words, the underlying contradiction that the Pharisees embodied was that they really did not accept John (as he ultimately went over to the Sadducees) but took over his converts and made them Jews. We must think that this 'baptism' swelled the ranks of the Jews at the beginning of the Common Era but ultimately led to the disastrous conflict with Rome (as Josephus's account lays blame on these same proselytes and the influence of the Helena Queen of Adiabene and Monobazus).
“Finally, from so little sleeping and so much reading, his brain dried up and he went completely out of his mind.”
― Miguel de Cervantes Saavedra, Don Quixote