Interesting question:

As a Rotarian I have to be above all the petty corruption
As for myself and my own Moral Compass, then I despise corruption in ALL its forms. If it were something petty I would not say a thing,however something major then I would not hesitate. However I would INFORM the person or persons its against before I take any form of action-to allow them to defend themselves. This is called the rule of law and I would NEVER go behind someone's back. They key here is so consult first then whistleblow.

The term, "whistle blower" to me indicates a serious offense involved, in which case, I have already blown the whistle, I have low tolerance. I am quite ruthless.

Likely the degree or harm of the offense... perhaps the risk/cost. Never being in that situation... a delima. I'd like to think in the extreme I'd do the right thing. Tough.

A lot of thought ahead of time.

Just the risk mostly but things like cruelty or murder and kiddy fiddling is a duty to me.

As a Fed employee...I am tempted every time I take ethics training (yes, we do!!) to point out the hypocrisy of taking Federal Govt ethics training these days.

Very difficult one as years ago I whistleblowed on a colleague and it all went wrong. Makes me reluctant but if you don't whistleblow something serious then you can end up in trouble. I would whistleblow on any form of abuse and bullying as a duty of care.

Not much. If an authority was saying one thing and doing something else, I'd be using a fog horn to draw people's attention to it. Whistleblowers are not snitches. They're holding the powers that be accountable.

Not a lot......right is right and sneaky, unethical, nasty etc needs to be called out!

Ethics outways all other factors, one reason I'm no longer a Funeral Director. I caught a preneed salesman overselling to a woman with dementia and turned him in. Was told I would never get another job as an FD, good ridence.

The calculus between the cost / benefit analysis and ethics depends on how great the harm is to how many people and/or to institutions and norms of society, plus my trust in the policing on this matter to actually be effective. It's one thing to be right, it's another to waste your rightness if the information you provide isn't going to be acted upon. Maybe bring covert retribution upon yourself in the process, without even eventual justice being served.

The only two times in my career where I've refused to conform to unethical requirements of employers or clients was (1) an employer wanted me to fire a truck driver for having a serious accident, despite that most of the blame was on the employer for wrongly running him illegally for 36 hours straight to make deadlines due to staffing and equipment shortages -- this could have cost people their lives and made me effectively complicit in murder if I had condoned the continuation of such policies in any way. And (2) when a prospective client wanted me to programmatically "cook the books" so he could decieve the IRS, which would have made me an accessory to tax fraud. In that latter situation I probably should have contacted the IRS and let them know that this attempted plot was underway but I was already cynical enough by then to imagine that the IRS would refer the matter around internally until it was forgotten, and that some other software developer would do the deed in my stead. It was enough for me to sleep nights, to not be a part of it myself.

Irrefutable evidence — because I have to know I'm correct, and I have to know that I'm not risking my career/safety/security for nothing.

A job as a ref

A good whistle?!?! Jk. I couldn’t resist!

Mostly just the ethics. Timing would have to be considered as to when blowing the whistle would be most effective at fixing the problem though. It'd also depend on whether it is more unethical than ethical or too unethical too justify. Many things aren't black and white, some things are both ethical and unethical at the same time, for example testing on lab rats for cures to disease and cancer and the like. Or observing corpses to better understand surgical anatomy.

A whistle blower for what... Murder or illegally downloading last week's episode of Murder She Wrote? (is that even still on?)
I think there's difference and it would depend.

If I knew of a truly illegal or unethical behavior and also knew that it was probable, I would be a whistleblower, readily. I have done it before -- without harm to my career.