I definitely understand what you mean. When I see another hurting person, and I try to help them, I can see very clearly that they do have worth and that there is hope for them to heal and be happy. It isn't hard at all for me to see the growth that someone else has achieved and to envision more growth in their future. For me, though, it's like I think I'm the exception to the rule. I'm the only one in the universe who actually and truly is completely hopeless, completely worthless, and can never heal.
I am working on overcoming those feelings in therapy, but they sure are a doozy.
I also completely agree with the other thoughts shared here. Some very insightful people have responded to you.