lcd - please note my comment about "Career threatening danger" was specifically "I know that declaring oneself 'unfit' to operate into discretion before it happens is fraught with career-threatening danger!" - not about "highlighting a safety issue" - 'refusing' discretion is not a safety issue. Certainly the "Captain should not have operated if he couldn't manage the duty" - not being 'fit' for discretion should be judged at the time it is required and can always be refused. It is not mandatory, although some managers seem to think otherwise.
Sorry to hear about your 'friend'.