Therin of Andor wrote:
Until the protomatter subplot was retconned into ST III, the main reason the new planet was so unstable was because, instead of the Genesis torpedo being detonated over the surface of an existing planet, and terraforming it, Khan exploded it inside the Reliant - and the device's program drew in material from the ship, its crew and the nebula gases instead... to create an entire planet.
A cop out if you ask me, that ruins the whole characterisation of David Marcus. In both TWOK and TSFS, there are many subtle and some not-so-subtle indications, that David is very much like Kirk, despite not actually knowing that he is his father. But there is quite a major difference between them, which makes the characterisation of David, brilliant.
David has the "leap without looking" attitude of Kirk, demonstrated by his willingness to run off into the middle of a jungle, in the pitch black of night, to recon a hostile group. The same attitude is what gets him killed, as he throws himself at a Klingon and engages him in combat, to protect Saavik and Spock. Had it been Kirk who had been in his place, Kirk would have not only survived the hand to hand combat with the Klingon, but he would have probably taken out the Klingon party as they were searching for the science team.
The point is, is that David lacked the finesse, skill-sets, and experience that Kirk had in abundance. They had similar attitudes and personality traits, but where Kirk would take risks, that would pay off, (even if they went wrong at first) David took risks, and always suffered the consequences.
The failure of Genesis should always be down to David taking a huge gamble with protomatter. It preserves his character, and the tragedy that goes with it. It also preserves those similarities and important differences, when comparing him to Kirk.