I think it helps to consider _what_ Jesus is talking about and _who_ Jesus is talking about when he issues his either-or.

WHAT IS JESUS TALKING ABOUT?

In both passages the background issue is the authority by which Jesus casts out demons.

Jesus is not addressing those who believe that demon possession is not real. Nor is He addressing those who think that demon possession is real, but the subjects of Jesus’ exorcisms were not demoniacs at all, but shams.

Accepting demons, demon-possession and exorcism is a bitter pill to swallow for modern/post-modern readers of the Bible. But if you swallow it, I think that it becomes pretty obvious that there are only three powers that could be at work here, and therefore only three powers that could make a demon leave:

1. The Heavenly Powers: God and His angels.
2. The Hellish Powers: The Devil and his other demons.
3. The will of the possessed person himself.

But the very fact that the person is _possessed_ means that the demon has overmastered his will. So that leaves 1 or 2. Either you think Jesus is acting on the authority of Heaven or you think He’s acting on the authority of Hell.

WHO IS JESUS TALKING ABOUT?

In the passages where he says “If you’re not with me, you’re against me”, He’s talking about Priests who were saying that Jesus cast out demons, not by the authority of God, but by the authority of the Devil. Jesus’ is clearly responding to people who are against him. Thus he issues the more exclusive formula.

In the passages where Jesus says “If you’re not against me, you’re with me”, He’s talking about individuals not traveling with Him and the disciples who were nevertheless casting out demons in the name of Jesus.

These alien exorcists clearly do not think Jesus was casting out demons by the authority of Hell. The disciples had a problem with them because they were not part of Jesus’ ‘entourage’. Jesus’ uses the more inclusive sounding formula to indicate that he doesn’t care about that, and that he recognizes that they are on His side.

I would phrase it not as moderates, but “people who are neither clearly for nor against.” In the case where allegiance is ambiguous, what should be concluded?

The reasonable answer is that if there are only two sides and which side is unclear, Christians should reserve judgment. But Jesus gave clear answers in opposite directions.

The point that technically the texts say exactly the same thing seems correct.

However, if we read the text technically then we miss the nuances, the hints and implications, and on a reading more sensitive to these the texts do seem to contradict. Matthew and Luke 11 may not say it explicitly, but they do imply that there’s a group of people who aren’t actively opposing Jesus but who are passively opposing him; Mark and Luke 9 may not say it explicitly, but they do imply that there’s a group of people who aren’t actively supporting Jesus but who are passively supporting him.

As it would be the same people who are neither actively opposing nor actively supporting Jesus, the passages say of this one group of people both that they are passively opposing Jesus and that they are passively supporting him. This looks a lot like a contradiction, even if the words used to express these ideas are logically equivalent.