*Disclaimer* The following is rendered rapidly and in conversational style, so if the precision is not up to snuff, it gets more work later on. Even if no single reason stands as reason enough, the collective force of it perhaps at least merits pause.
Twelve Reasons to Hold Scientific Determinism (a.k.a. brain science) at Arm's Length
1. Consciousness is movement and not determinable thing, hence it has no meaning in its isolated parts or mechanisms. Even if brain science locates things inside the brain that appear as evidence for this or that, there is little way to tell if experience itself did not make the impress prior to the trail it left as evidence. (conditions)
2. As movement, consciousness is of an indeterminable size/shape/quality, until it has 'completed' that movement. As long as the being is living, there is no such completion, and hence, no determinable shape in which to state its fullest nature. (the open-ended nature of consciousness)
3. Heisenberg's Uncertainty Principle: Before science can look into the brain, it has to have something to look for. It will find it. And that's all it will find. Into this category, we can find poured the innumerable agendas that every scientific endeavor must set itself up with before it can endeavor at all.
4. The Problem of the Thing Looking at Itself: In such a scheme, the instrument is trying to measure its own instrumentation, perhaps with the assumption that it can exceed its own instrumentation in order to find out things about itself.
5. The pursuit of physical components to locate immovable, material, innate characteristics in the human being is similar to searching for the god-seed. The danger in this approach is as pernicious as in that of all religious fundamentalists, and equally serviceable to dogma and excuse.
6. Consciousness is nothing until it is moving in exchange with the conditions (world) that make it move. In this molten exchange, 'external' conditions are at every moment creating consciousness, just as consciousness is taking in and forming a world for its grasping. As in #1, attempts to cut across that movement/exchange will be about as useful to the person who wants to learn about human thinking, as is a photograph of a person running is useful to the person who wants to learn to run. Yes, something in the way of information, or form, will emerge, but it will never be the complete picture. It might even confuse the complete picture.
7. Because of the molten nature of the consciousness/world exchange, what scientific determinism will hold as rule for one cannot be held as rule for all. Each organ of consciousness occupies and is influenced by its immediate surrounds, and as we seem to see, no two things can occupy the same place at the same time. Even if we are sitting next to one another on the sofa, the one closest to the fireplace will have a different experience/impress of the world than the one sitting farther away. Any rule-of-thumb that human determinism can give us must fall back upon the individual, rather than the species, anyway.
8. Scientific Determinism is the uneasy bedfellow of all beliefs (or rather disbeliefs) that deny the existence of any sort of human agency whatsoever. Like 'no-self' buddhists, human beings are the passive substance in a chain of cause and effect, rather than the conscious generators/originators of any effects themselves. This, in a sense, is a denial of the self-same consciousness that scientific determinism is looking for. Further, it ignores the problem of individual consciousness as mentioned in #7. Even if scientific determinism can explain via the chain of cause and effect what led this particular individual to do this particular thing, it is still, and will always, be stuck dealing with this thing one-by-one.
9. Pure Scientific Determinism gives you no wiggle room at all to discuss choices of any kind. No more "some things we can choose and others we can't," etc. All sense of choice falls entirely under its axe.
10. Being as Scientific Determinism is unable to transcend the problem of individual consciousness and its immediate conditions, it will only ever be able to say something about an individual, and not human beings in general. We could, like many do, hand over an understanding of our individual selves to the therapist (i.e. let others declare the nature of our natures for us), or we could do the work ourselves. Because of the conditions mentioned in #6, we can become more conscious creators of and in this molten exchange.
11. The presence of warts were once supposed to identify the witch; the lack of height to identify the dictator; the large proboscis to mark the endowments of the donjuan; the presence of breasts - a block to everyone's brain. Now we can see brain waves and tiny rents and wrinkles in that brain. Every bit of it ought to be approached with a healthy skepticism that the mistaken assumptions of the past might have taught us. The mechanisms alone are meaningless in light of the world they mechanize with. It's like peering inside a watch to find out how it works, and assuming you are going to come away with an understanding of time.
12. If we are to err on either side: the side of immovable/material/destined consciousness [i.e. determinism]; or the side of open-ended conscious possibility, I should like to err on the latter side in every case. In the spirit of Leyla's chicken stories, I have a "squirrel-proof" bird feeder in the yard, but since the squirrels don't know that, they're getting up there anyway.