10 Darkest Star Trek: Enterprise Moments
4. That Time Phlox Let A Whole Species Die
One of the best parts of Enterprise was that we got to see the beginnings of many famous Starfleet philosophies, including The Prime Directive. In the first season episode Dear Doctor, the crew encountered a pre-warp society that was already aware of alien life (apparently they had met the Ferengi in the past). This society was made up of two species: the Valakians and the Menk.
The crew discovered that the Valakians were dying of a mysterious genetic mutation that would kill them off within two centuries, however, the Menk were immune to this pandemic. Despite quickly coming up with a cure, Dr. Phlox and Archer chose not to give it to the Valakians for the strangest reasons. They argued that they couldn't 'play god' or interfere with nature, but as Archer correctly argued, every time you do medicine, you're interfering with nature. They also suggested that the mass death of the Valakians could allow the Menk to prosper, as they were oppressed by the Valakians at the time and treated as little more than pets. Phlox described the pandemic as an inherent flaw in Valakian DNA, yet it clearly wasn't since he developed a cure for it…
Why could they not just strike a deal to supply the cure in exchange for the liberation of the Menk? As T'Pol said, they had already encountered alien life, so the cultural contamination was minimal, plus the future Prime Directive would eventually allow for exceptions to save an entire civilization. Instead, the Enterprise simply gave them medicine to ease symptoms and flew away, leaving the Valakians almost certainly doomed and the Menk no better off.