I couldn't disagree more, sorry to say. Our positions seem totally irreconcilable.
"humans have thought structures that they mistake for reality, i.e. they think their brain is a non-distorting medium that transmits full reality, and this produces delusion."
You're either misunderstanding science, or possibly confusing science with something else. This position doesn't square with the accepted definition of science, or with my personal experience of science. Science is "a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe." [Wikipedia] But I've already stated this previously, and restating it is unlikely to help matters.
"So real Buddhism is its own kind of science, and critiques scientific positivism as a thinking structure that is delusional."
I don't accept Buddhism as any kind of science, because it's not falsifiable.
"I think determinism is one of those thought structure delusions."
Again it's a dead end. I like to use the example of bacteria in bottle. Assuming an unlimited supply of nutrients, the bacteria will fill the bottle and choke on their own waste, every time. In fact we rely on this deterministic outcome to make alcohol. In science, determinism isn't a philosophy, it's simply a description of a situation in which the output for a given set of inputs is known and repeatable.
"We can't imagine how we could have failed to come into being."
Individuals may believe this but it has nothing whatever to do with science. Physics and astronomy routinely explore situations in which we couldn't and wouldn't have existed. Genetics proves conclusively that evolution doesn't converge on anything except fitness for prevailing conditions. There is no top or bottom, and malignancy is as natural as anything else. Life evolved from bacteria, and regardless of what people do or don't do, life will return to bacteria: only the timing is in doubt.
"But the problem is that determinism leaves us totally helpless,"
Not really. Unlike the bacteria in the bottle, we can choose not to choke on our own waste. The outcome is only determined on the macro timescale, i.e. hundreds of millions of years. As I tried to express in "Less," the main variable in play is the degree of suffering we're willing to inflict on future generations. My personal point of view is--and has always been--that humans are quite capable of inflicting maximal suffering on future generations. Recent events provide plenty of support for my position, but that doesn't make it deterministic.