1.) Assumption: Objects and events affect our thoughts and beliefs. The determinist believes this, because it must be an object or event which determines thought. The non-determinist also believes this, because to think about something is to be influenced by it. Thus, everyone accepts that there is some influence over our thoughts on the part of external factors (debate being over its degree).
2.) Either your thoughts are deterministic, or not. (Excluded middle)*
3.) Plantinga has argued against thought determinism -- in that one cannot claim to have arrived at this belief through reasoning.† If determinism is true, you can't be correct about it (in contrast to being wrong about it) -- you are merely 'caught up in a particular causal stream.'
∴ If you believe in absolute determinism, there is no sense arguing. You might still argue (you would be fated to do so), but there is no sense in it.
From somewhere in my pile of notes, on one of the myriad pages of semi-waterproof paper I use when an insight strikes me in the shower -- pages that should eventually make their way into my commonplace book, is this fragment:
The "objective" or "scientific" study of religion is the attempt to answer (without ever asking) the question, "Why do so many people believe the wrong thing?"
Every so often, I do something like this to myself. What on earth did this guy mean? And if he doesn't know, how does anyone else stand a chance? On reflection, I think I understand now what I meant, and I will boast that, if taken seriously, it would upend religious studies, and anything downstream of it -- which is most of the academy.
I write about all sorts of things. This is one of the places where I do it.