I would like to thank Judicator and Pfad for their arguments, as they have helped me to formulate the following argument and find more clarity about this issue.
Deterministic Materialism is the view that ultimtely everything in the universe can be explained via material cause and effect sequences, even if those sequences include some random factors. IOW, whatever I think is ultimately just the result of some kind of cause and effect from material substrate. Molecules clang around, so to speak, and I decide to go to church. Other molecules clang around, and someone else decided there is no god.
This presents a problem in arguments, because arguments are necessarily about making (or attempting to make) true statements, or evaluating statements for their truth value. "Truth", in this case, is about the rational nature of how inference are drawn from premises to reach conclusions.
This process of making and discerning true statements must, in order to be coherent, be made either deliberately, or necessarily. If true statements are made by chance with no means of deliberately or necessarily evaluating them as true, then our evaluations of them are also chance. Without some means, some where, of making deliberate or necessary true statements or evaluations, then all we can hope for or chance, and not coherent correlations of statements to truth.
Essentially, if left to chance, we'd be like monkeys banging on keyboards; every once in a while a monkey would write a true statement, and every once in a while another monkey would agree that the statement was true - not deliberately, or necessarily, but by chance. Thus, the framework of true correlations would be incoherent.
From a deterministic materialist perspective, "deliberacy", or free will, is caused by necesary and chance forces, so there is no true "deliberacy" in the world. All they have left are chance and physical laws to produce true statements. Chance is insufficient to make coherent true statements, so we must turn to law.
If physical law necessarily produced humans that made true statements, then all humans would make true statements all the time. We factually know this to not be the case. The materialist might argue that chance intervenes and redirects humans into making false statements; the problem here is that there is no deliberate means by which we can distinguish between necessarily true statements and chance untrue statements, because we have no true deliberacy; our deliberacy is produced by both necessary and chance factors, which may result in flawed reasoning when we attempt to discern true statements.
This is the conundrum the determinstic materialist faces: they have no means by which to expect to make true statements, or discern them, except by chance - making their position - logically - necessary incoherent.
Their position might be true, but they can only argue that if it is true, then they have arrived at that position by chance, because they have no deliberate or necessary means by which to discern or argue its truth. They have no coherent argument as to why it is true; if true, it is only true (from our perspective) by chance, and not by deliberate reasoning or necessity.