Yeah, but I don't have any reason to think the CIA's involved...
Well what would constitute a valid reason for thinking that the CIA were using undetectable thought rays? What do you think constitutes a valid reason for the believing that a disembodied spirit is responsible?
I've always thought of it as an underlying nudger rather than an all out controller. The mind controls the body and its actions, the spirit influences the mind, but so does the brain (because the mind stems from the brain). And I suppose the spirit can be affected as well... from the phyical world, to the body/brain, then through the mind on to the spirit.
You seem to be claiming the 'mind' as some sort of intermediary between the physical and the immaterial spirit. I am intrigued by this idea and how you see it working.
Given the example in the OP what do you think happens to the spirit as a result of the physical tumour? Anything at all? Is this spirit self a version of 'you' that is free from all physical effects? Or just some? Is it a version of you that is free from behaviour affecting hormones (e.g. testosterone)? Free from disease (e.g. alzheimers)? Free from the effects of ageing? Free from the effects of all physical experience?
Is this spirit version of 'you' something that exists unchanged your entire life? If it does change then what things cause it to change and what things don't? How do you decide?
Maybe this subject should be in the religious section because what you are arguing certainly isn't biology. What you are arguing is that you have no idea what free will is and are trying to find a physical attribute that refutes a non physical thing.
A lot of this comes down to 'them and us'. Dehumanisation is a common psychological method of making horrific acts more morally acceptable to those who commit them.
So you can argue (as I think you are doing) that we have an innate evolved sense of morality whilst also accepting that we don't always apply it consistently.
We apply morality to 'us' and are much more flexible about applying morality to 'them'. But how exactly we determine who constitutes 'us' and 'them' in any given situation s far from simple and has it's roots in other evolved aspects of behaviour.