@Impel:
No, he wasn't feeling useless or weak, he was scared because he know the Admirals or the CP9 or someone would come and rape them up the ass.
You're arguing with exactly what he said in the manga. He felt weak. He said so. How can argue with exactly what he said (AKA What Oda said)?
Usopp has low self esteem. Getting the snot beat out of him by the Franky Family did not help him feel any better about the situation.