If he was tested, he might find out he had a disease, and then he'd be accused of knowingly endangering others if he didn't tell them about his disease. If he isn't tested, he'll only be accused of not finding out that information, which is often considered less serious. [emphasis added]

This strikes me as being a major societal bug. I agree that it's in the short term interests of the person to avoid getting tested. But, many people avoiding testing and thereby creating a pressure that it's normal and okay to do that, is what causes the silly situation in the first place.

A lot of the other scenarios you write about seem similar: strategic ignorance can be helpful for the individual in the short term, but a general policy of deliberate non-ignorance would be better for everybody overall.