I suspect the reason he refuses to undergo psychosexual testing is because he suspects that he may present as having a psychosexual disorder.
The problem here is twofold: interpretations into the revelation of possible motive for masturbating during a murder trial, and significantly the stigma of being diagnosed with a psychosexual disorder. If this were not present, more lasting help might be at hand to manage Thompson's behavior, which could be considered under any number of umbrellas of psychological/neuropsychiatric presentations, regardless of whether one need diagnose him or not with anything from a frontal lobe lesion to simply being a dick.
Interestingly, every poster here presumed that the actions here were done wilfully and thus that Thompson's behavior was the result of rational, conscious consideration. Interestingly, Brossett's statement indicates that she is somewhat aware of the broader issues at hand for Thompson. Insanity, I don't think so, but definitely there is some ground to stand on there that Thompson would rather deny (and Brossett would rather confirm).
As a doctor-to-be, I would urge some caution, maturity and consideration on the nature of rational conduct, motive and the stigma of psycholigical disorders, as well as the arbitrary nature of diagnoses.
