Man do I take issue with that first attitude. Even if he's right and karma eventually gets back to cheaters, that could be years down the road after they've wasted a medical school slot and with much higher stakes than being busted in a college class. But universities do set profs up to be apathetic - they should be able to immediately hand off suspected cheating to an impartial committee not deal with it themselves. Plus they should not be paid based on their student evals, which already punish profs for giving reasonable grade distributions instead of straight A's or large and challenging assignments instead of simpler or easier tests.
Pretty funny that cheating was at like 20+% though. I think I come off as very jaded and cynical on this topic but seriously, academic integrity policies are just not a strong deterrent. Talking to my friends about this stuff (who generally don't know my opinion) most people would take advantage of low risk cheating opportunities like having access to pics of the exam ahead of time.
The thing is in some ways they are too strong of a deterrent for the policies to be utilized effectively. I served on my schools judiciary committee jr and sr yr. I didnt have a major role at all(I was at the bottom of the food chain being a UG) but I got to see how these policies were implemented and more importantly I got solid insight into how professors viewed these incidents and decided to pursue them.
Ultimately the best way I can summarize what I gleamed from my time on the committee and doing my own research into the issue is many professors at the end of the day just arent comfortable making decisions that single handedly ruin students careers. Whether you agree with or not, many professors just arent comfortable with it. There is no in between for academic IAs and my sense is talking to some professors is there would be more willingness to pursue academic dishonesty if there was some in between. With the system in place at my school, its basically if you report it to the dean its a slam dunk IA that ruins those UGs careers. Professors I know have said they wish there was an in between ie a student gets disciplined say "loses financial aid but doesnt have an IA" or "has to drop out of school for a semester" or "has to sign a contract if they cheat again they get expelled and still have to pay tuition for that year" but without them having that IA to destroy their future. Again this is just from what I've gleamed. Obviously I dont agree with all of it, but professors arent always huge fans of hte idea of some committee often full of young adults deciding a UGs entire life like this. So they take it into their own hands ie "do I think this IA is worth ruining someone's life over?" In many cases, they don't. A couple professors in particular have told me when you compare somethings that people get into med school with such as DUIs or vandalism I dont see "copying a solution guide for HW" or "using your friends participation clicker while there in the bathroom" "or working together on HW" or "seeing someone with wandering eyes on an exam" as worse than those or worth ruining a career over. Again, it's their personal choice but the way the system is set up that they feel like they want to be the ones making the choices, not a judiciary committee. Whether you agree with or not, that seems to be what I and others who were involved in this picked up on over the years.
I do agree with your last point that I think if you put a fair number of pre-meds in a pressure situation and they were handed a pic of an exam beforehand that was taken illegally, they would glance at it and use it to their advantage. Likewise, there was a thread a few weeks ago about how someone was emailed a copy of an exam they got from a professors desk. I think there are a solid number pre-meds(including honest, noble and good natured ones who would make good doctors) who if they got that email wouldnt turn in their friends. They might not look at it and engage in an email convo like that poster did, but they wouldnt turn them in. If in fact their friends got caught and the email was found, they would be on grounds for an IA if they hadnt turned them in. So these things can be a tricky situation and there are different degrees of an IA. I would look at someone getting their acceptance revoked for "not turning in friends who stole an exam but they themselves didnt use that stolen exam in anyway or were at all involved in it" differently from someone getting an acceptance revoked for plagarizing or stealing an exam.