You have a point, this might help test the resistance to jailbreaks for example. There are probably better tests for that than OOC roleplaying, I think. At the same time, what you expect is likely not going to happen due to many reasons (e.g. can't optimize for two contradicting objectives), and harness design offers a practical workaround that is being used for years already and is reliable unless the user is actively trying to jailbreak the model+harness.