You're never a worser person if you can't help someone. In fact, you're gonna be just as good as when you actually help them.
Cuz when you know you can't help someone, whether it be a personal reason or otherwise, you're being more thoughtful to them than being selfish cuz you're focused on your reasons. Cuz knowing you can't help is knowing your limits.
Imagine if Yui actually went to sing in the choir, if she goes and she fcks up because of her trauma, it might ruin the entire choir, for her and for everybody else.
You're as good a person when you know you can't help than when you do, just make sure the reason is truly justifiable and it provokes thoughtfulness to the party that needs said help when the consequences of helping them goes south cuz you actually couldn't.