I understand the sarcasm/joke intentions, but this is just a slight pet peeve of mine with what the "professional" instructors tout as the mantra in the industry.
I don't think its necessarily all instructors or necessarily an industry-wide deal. I do know what you're saying though. The majority of instructors will probably say concealment is a good idea.
It's premised on the assumption that you're more likely to be a bystander to a violent crime than the intended target.
I don't think that's necessarily true. I think its based on the idea that, even if you are the intended target, displaying the gun forces the situation along the force continuum much more quickly. It is possible that displaying it will cause the assailant to move along to the next potential victim to avoid that end of the continuum and you'll never know it. It is also possible the assailant will see the gun and realize he needs to act decisively and with significantly more agression against you, and you'll never know that either until its happened. I think these instructors are viewing it in terms of that risk. There are two components to measuring risk. Probability and severity. While the probability of the second outcome may be smaller (though, as you mentioned, we have no data on which to base that assumption), the severity would be much greater. Greater even than if you'd not displayed the gun and left yourself more options with which to deal with a less decisive and less agressive threat.
Please note, I am not making an argument either way. I am just saying it could be seen this way. I don't think pro-concealment instructors are assuming you will only be witness to a crime. I think they are saying that you will be the victim and above is how they may weigh the risk of concealment vs open carry.