^Good lord, we're not talking about a regular plug and play fusion device here! It's COLD fusion
technology. It's a whole different ball game!
I think the point of the entire scene was to show that these were still kids playing with adult things.
So the kids get a pass because Starfleet had the poor judgement to give them the flagship to play with in the first place. Incompetency at the highest levels of SF Command? Well, I guess that does follow tradition. So, whereas in the past Our Heroes™ were the smart ones and the Admirals were stir crazy, now the whole lot are idiots.
So what did nuKirk actually do wrong?
He saved a pre-Warp civilisation from death instead of watching them die.
He should have thought - What would have Picard done in this situation? He would have let them die and then lectured Data about it.