You make some good points, but I disagree about the interest in true crime stories and trials. These are about the only occasions left when people are able to make judgments and discuss issues of morality.
No argument that the Natalee Holloway story was overdone, for example. but the case hit home because a lot of parents realized that they would have let their daughters go on this trip.
As for O.J., the judge and the prosecutors allowed the proceedings to become the trial of Mark Fuhrman and the LAPD. The jury was subjected to personally intrusive grillings before they were impaneled and then sequestered for an unconscionably long time. When you do this to people, I'm sure they begin to identify with the defendant and resent the legal system.
However, entrenching these stories in a network and a regular show on Fox has meant that the producers actively seek out their next big story, and often trials are blown out of proportion to the evidence, resulting in media circuses (the Duke case) and perhaps innocent people suffering (Duke rape case).
Also, it hasn't escaped me that if Natalie Holloway had been a buck-toothed, acne suffering brunette it wouldn't have been much of a story. And if Lacy Peterson had been a chubby black gal from South Central, we wouldn't have heard a word about her.
While some people with intelligence and sensitivity may draw the conclusions from these shows that you suggested, I think more often they are simply entertainment for the public and revenue-producers for the networks.