^^^Call it a chain reaction of events. If Kirk hadn't taken command, Spock might not have been there, and McCoy definitely wouldn't be there (however inconsequential his presence was). Decker might have been distracted by Ilia's presence on the bridge and made the wrong call during the "lightning" scan. That might have caused Enterprise to be digitized, and there would be no one to decipher V'Ger's origin, and no one to enter the transmission code. Earth would have been destroyed.
So maybe sometimes a little hubris ain't so bad.
EDIT: Now that I think about it, showing Kirk to be out of touch (growing old?) might have been the inspiration for the theme that continued through the next several movies. Maybe, maybe not, but it's something to consider.