I just started working at a research hospital. One problem I've heard mentioned from several people is the difficulty of getting black patients to participate in studies or even consent to having their biological samples used for research. If you think this is "illogical", then you're probably (1) don't belong to a lower status group in American society and (2) haven't read much about the history of medical experimentation. Tuskegee wasn't an isolated incident, before the advent of modern consent & ethics standard, medical experimentation in the US preyed on the lower rungs of society.

Some examples:

* Holmeburg prison: http://www.amazon.com/Acres-Skin-Experiments-Holmesburg-Pris...

* Development of modern gynecology through live experiments on slaves: http://en.wikipedia.org/wiki/J._Marion_Sims#Medical_experime...

* Whole-body radiation exposure experiment in the 60s: http://articles.latimes.com/2007/oct/06/local/me-saenger6

* Immortalized cell line from Henrietta Lacks without her permission or that of her family: http://en.wikipedia.org/wiki/Henrietta_Lacks

and, of course, there was eugenics: http://en.wikipedia.org/wiki/Eugenics_in_the_United_States#C...