Maybe if Kirk just left them there that'd be one thing, but shooting them when they're in the middle of being destroyed by a black hole? That's not really called for.
"... and so I allowed the
Narada to be consumed by the black hole."
"Thank you for your report, Mister Kirk. Now, I have some questions for you."
"Yes, Admiral?"
"The
Narada."
"Yes, Admiral?"
"Romulan starship from the 24th Century."
"Yes, Admiral."
"From the year... 2387, is that right?"
"That is what our intelligence indicated, Admiral."
"So it was 129 years more advanced than anything the Federation has ever encountered. Does that sound about right?"
"Yes, Admiral."
"And this ship... the
U.S.S. Kelvin encountered it in 2233, didn't it?"
"Yes, sir."
"It had, in point of fact, just emerged from another black hole when it destroyed the
Kelvin, hadn't it?"
"Yes, Admiral."
"Tell me, son, are you an expert in 24th Century Romulan technology?"
"Sir?"
"You heard me. Are you an expert in 24th Century Romulan technology?"
"... No, sir."
"I see. Do you at least have, say, a passing familiarity with 2380s-era Romulan technology?"
"No, sir."
"No? Never took a class on it? Never took Intro to Alternate Future Alien Technology, Romulus Edition?"
"No, sir."
"I see. And... tell me. This Nero fellow. You offered him humanitarian assistance, did you not?"
"Yes I did, sir."
"Very good. Well you should. And this Nero -- he refused your assistance, didn't he?"
"Yes he did, Admiral."
"And in point of fact, he declared his eternal hostility and made it clear that, if he could, he would still seek to attack Federation starships and planets, didn't he?"
"Yes, sir."
"So, if he had escaped, he would still be a major threat to Federation security, wouldn't he?"
"Yes, sir."
"So... Let me see if I have this straight. Instead of firing upon the incredibly dangerous starship of an avowed enemy of the Federation who had made it clear that it was his continuing goal to commit genocide against every Federation world, you allowed it to be consumed by a black hole -- even though you have no idea what a 24th Century Romulan starship is capable of, and even though that same ship had already demonstrated an ability to survive passage through a black hole 25 years ago?"
"... Yes, sir."
"Thank you,
Cadet Kirk. That will be all. Report for duty aboard the
Enterprise at 0830 hours. Captain Spock will be needing someone to scrub those plasma coils."