> But does the professor have a deontological obligation to catch cheating, and to make a good-faith effort to have fair outcomes in which students who studied and understood the material receive better grades than cheaters?

Most courses are either graded on a curve or the material is adjusted in difficulty to target a certain level of challenge.

When cheaters come in and destroy that curve and inject false signal into the difficulty feedback loop, the non-cheaters suffer from increased difficulty.

So yes, there is some obligation to keep the playing field fair and accurate.

Given that grades can have an impact on real-world outcomes (e.g. admission to a desired graduate program) then it’s possible that allowing cheating can have broad impacts beyond the students. Imagine if you took some 4.0GPA students under the assumption that they actually learned what they claim, then discover that they have no idea what they’re doing because they cheated the whole way.

Also, the mind boggles at the suggestion that catching cheaters is bad because they might face some consequences for their dishonesty.