It's what anyone with a backbone does.
Really?
Wonder how the cowardly little Jimmy Kirk described in "Shore Leave" was ever tapped for command, in that case. For that matter, how did he ever get into the Academy?
I suspect that if Starfleet Academy used West Point or Annapolis as a model, a cadet who assaulted an upperclassman -- even one who regularly tormented him with practical jokes -- would very quickly find himself dismissed from the Academy, with no possible future as a Starfleet officer. It would be easy to view as a better man the Kirk who
resisted the temptation to retaliate, keeping his focus instead on the goal of a Starfleet officer's commission, than it would a Kirk who forgot his place in the defined hierarchy of Starfleet Academy and washed out in a disciplinary action.
It has nothing whatsoever to do with size or strength -- nothing to do with the
ability to strike back; upperclassmen are superior beings by definition and a plebe in Kirk's place would be expected (within reason) to take what was dished out by someone higher in the chain of command. Practical jokes (
not bullying -- bullying is stated nowhere onscreen) are what he had to suffer, and that he did so patiently even though he
felt like getting even is part of what allowed him to become the Captain Kirk we saw on television every week. Patience, rather than thinking with his fists:
that's where the "backbone" lay.
At least that's the way I always read it, even the first time I watched the episode on its original run.
Edit:
Responding to Starship Polaris. Actually he is everyones president now whether we voted for him or not.
He is every American citizen's president, but that is not really a topic for discussion in this forum. If you wish to discuss the content or sentiment in someone's signature line, PM would probably be a better bet, or raise it in one of the threads in Misc or TNZ more suited to the topic.