Credit scores aren't an indicator for morals. Do you really have so much faith in the current credit system that you'd be willing to turn someone from a job they're otherwise qualified. The argument could be totally flipped on it's head. It's important to hire someone with a bad credit score (using it as a measure of wealth apparently) because they will value their job more and not do anything to risk losing it.

I didn't say credit scores are an indicator for morals or wealth, or that they're a system I support. But bad debt is a possible incentive to act against your employer's interest that can be controlled against by using credit score as proxy for knowing their exact financials. I'm not saying that's fair, or good, just that that's the thought process behind it.

Is there direct evidence this is true or is it just a "common sense" thing that makes sense but might very well be false?

Do you mean evidence as to whether people with lower credit are likely to do such things against the company's interest? If so, I'm not sure. I just know it's something that is considered for govt purposes re: security clearances and that logic seems to carry over to private sector.

Before I or others go looking for such, what would you consider an acceptable standard of direct evidence?

I honestly don't have an opinion on it. It just seems something that's repeated and accepted often and I'm being skeptical is all.

I will probably look into it myself too! So whatever you can add to the discussion is great :)

I feel like "compensate them appropriately" should be the actual solution to this problem.....

There are real enforceable legal salves you can take for these purposes included targeted NDAs (as opposed to the less enforceable "Don't talk about our stuff") that makes it really easy to prove wrong doings - additionally there are forms of business insurance out there to cover the short term sudden costs of corporate espionage/sabotage.

Basically, trusting in the person to be trustworthy because equifax is giving you a big thumbs up with a stupid grin on their face is a stupid idea. Just set up protections for your company, properly utilize the practice of minimum access and call it a day.