It's a straw man very simply because at no point was anyone proposing that be done. The answer to the question "are we talking about mothballing the Starfleet" was clearly "no." And that's the purpose it was supposed to serve in the script, at least one draft
of which simply called the character "A MILITARY MAN." Remember that the debate was supposed to mirror that over changing relations between the U.S. and U.S.S.R. in the real world, and the conflict in the film was between those who felt there could only ever be a military solution and those who realized (initially in Spock's case and ultimately in Kirk's and others') that Starfleet's mission had "always been one of peace."
Regarding offensive vs defensive capabilities, can't the same equipment basically be used for either? It's how
it's used that makes the difference. And I don't think SF has ever been portrayed as being particularly oriented towards taking the offensive. (Section 31 and overzealous rogues aside.) Almost all of the combat scenarios we saw involved an outside aggressor who started the conflict. Yes, once the tides of battle in the Dominion War turned in their favor they went on the offensive, but this was still in response
to the threat the Dominion posed and the fight they started, and moreover was done in coordination with Klingon and Romulan forces. It never seemed like a situation SF sought or were particularly suited to. And really, more often than not, when SF comes up against a powerful enemy in open combat they get their asses handed to them, or are saved only by a last-ditch effort.