Yeah, Courage is like that, but how would you fight? Its not like those morph capable people will trust you the morphing power to fight alongside them. After all, you might be a controller just asking for morphing power.
And its not like you can directly attack the Yeerk Pool or base either, You would die ten minutes before you got to the entrance. How the hell will you get high calibre guns and explosives to blow up the Yeerk Pool Anyway?
Plus, the courage thing. Sure, Courage is beating your fear even if its there. But I doubt anyone could suddenly jst fight that fear. You will see what I mean when you know you are about to get KILLED. NOT DIE. KILLED. You really don't know how you would just love to beg to your killer, "Please don't kill me." Believe me, I've been there. Not that easy. The Animorphs were forced to fight because they were haunted by knowledge and responsibility, recieving the powers. They had no choice, plus they can defend themselves.
If it was me, I would try to help too, but not Rachel style. After all, I use my head, I know I can't directly fight the Yeerks Rachel style. Like, be a food supplier for soldiers. Or just plain hide. That would be the most probable reaction I could do.
Anyway, if the Yeerks win, humans will have a choice either to get burned by Andalites or be slaves of the Yeerks. That would be time for suicide.