Replies, so far, seem to indicate two viewpoints - 'whistleblowers are poison' and 'whistleblowers save lives'. The first view is almost standard in British society, particularly business. The second requires strength of character out of all proportion to the good it can do.
From (personal) experience - 18 months with the same alcoholic captain, in a VERY steep cockpit 'gradient' sharpens ones reflexes greatly!!
From (personal) experience - recovering one's predecessor's personal effects from the crash site where he was killed by a 'known' irresponsible 'cowboy', makes the Boss's assessment "that we were ALL to blame, because we knew ... and did nothing!" a simple truism.
"Never grass up your mates" may well be a survival essential in criminal circles - it has NO place in any sort of RESPONSIBLE working environment.