I thought I remembered that the Public Health Service intentionally infected people in order to see what would happen, but Wikipedia seems to say that they intentionally withheld treatment from people who were already infected and deceived them about this, rather than causing the infections themselves (although some of the study subjects spread the disease to other people during the course of the study, which were new infections that could have been prevented by treatment).

Isn't the net result similar anyway?

1. People who should have been treated weren't.

2. As a result of #1, more people would have been subsequently infected.

Additionally:

3. Distrust in healthcare is engendered amongst a marginalized population, with potential to lead to further incidences of undiagnosed ailments.

The net result is similar, more people are infected than would otherwise have been. Just because the infection mechanism is less obvious doesn't necessarily make it less bad.