I'm interested in learning about how Biblical Unitarians arrive at the conclusion that Jesus is not God from a deductive reasoning standpoint (for examples of deductive arguments, see this question). I'm particularly interested in the validity and soundness of their arguments. Is the argument valid? Is the argument sound? Are the premises of the argument properly justified? Is the argument rigorous in its use of words or is it taking advantage of the ambiguity in certain definitions?
There are a large number of arguments that can be made from a Biblical Unitarian standpoint that Jesus is not God. Although I am skeptical of deductive arguments such as you are looking for (and prefer multiple lines of probabilistic reasoning that point towards a conclusion, instead), here is one that is easily transferred to that format (taken from Jesus is the Son of God; not God the Son, a Biblical Unitarian site).
"Jesus and God have separate wills. Jesus prayed to God, “not my will, but yours, be done” (Luke 22:42 ESV; cp. John 5:30). If Jesus and the Father are the same “one God,” then they would have one will."
- God cannot have a will different from His own will.
- If two persons are both God, therefore those two persons will have the same will.
- Jesus and the Father's wills are at times different.
- Therefore, Jesus is not God.
Trinitarians of course can respond to this, by saying things like 'Jesus has two wills', one his divine nature and one his human nature. Only the human nature is in conflict. And so on, and so on (as the link referenced above goes on to note).
The question for me isn't whether any one argument is logically seal-proof (virtually no argument is, for anything), but how the arguments taken together weigh against the counter-arguments.
The major line of argument by Biblical Unitarians isn't that there are 100% deductive arguments in their favour (although I think some get pretty close, and requires a 'God is ultimately a mystery we cannot understand' response), but that the scriptural evidence strongly leans in favour of Jesus not being God.
Again, for argument after argument that Jesus is not God, you can see the page linked above. You could transform basically all these points into a more formal style.