It is mostly wrong because we are robbing Nero or anyone in his position of their remaining life and that hasn't been removed.
However small it is, there is a chance Nero could pull a rabbit out of his hat and survive the collapse of the Narada. If he survived (remember he had a collection of craft aboard), he could become a huge problem somewhere else in the timeline.
This sounds more like an argument that Kirk is wrong for simply doing something any other rational being would do in his place. It's not about the action taken, it's about whose taking the action.
I count seven photon torpedoes fired from that clip, four from the Enterprise
and three from the Excelsior
. with there being three separate firings (1,2,1 from Enterprise
and 2,1 from Excelsior
) and no one stopped to even give Chang the chance to surrender.