I'm not entirely sure why the Federation (or David Marcus) started declaring that Genesis did not work. Apparently phases I & II went off without a hitch. That should have atleast given some credibility to the science. I would argue that the Genesis Planet should not have disproven the technology either. For one thing it was never deployed in the way it was intended. Genesis was supposed to be deployed against a preexisting dead planet. The Genesis torpedo was detonated in the middle of a nebula with not a planet in sight. Thus Genesis, created a planet from the material in the nebula. Genesis was never meant to do that. Its hardly surprising that planet proved to be unstable.
At the very least, Genesis proved to be the ultimate weapon. Imagine if the Federation had been able to deploy that against the founders (who's home world happened to be a "rogue planet" sitting in a nebula). It might have been the Hiroshima type event that ended the war.
At the very least, Genesis proved to be the ultimate weapon. Imagine if the Federation had been able to deploy that against the founders (who's home world happened to be a "rogue planet" sitting in a nebula). It might have been the Hiroshima type event that ended the war.

That is what the Reliant was doing at the beginning of Star Trek II.
I'm sorry but you seem to have missed a huge huge plot point here. The Reliant went to Ceti Alpha because they thought it was a dead planet, they read an energy signal, and went down to see what it was. That's how they stumbled upon Kahn. Hilarity ensues.
