Why does Eric say "what is wrong with all of us"?

It isn't actually Erik who says these words in the story; it's his younger brother Paul. Whatever he does, Erik just can't seem to stop messing up Paul's life. When Paul's friend Tino comes over to hang out with him one afternoon, he and Erik get into an argument which ends with Erik giving Tino a good hard punch in the face. In fact, he hits him so hard that he knocks him flat out.
The following morning at the breakfast table, Paul's itching to tell his dad what happened. He's got the words all worked out in his head, but somehow they just won't come out. He sits there, watching his dad reading a newspaper, knowing that he must do the right thing. But he can't. That's when Paul reproaches himself for his inability to spill the beans:

Why couldn't I tell my parents about Erik? What was wrong with me? What was wrong with all of us?

Paul just can't understand why he can't come right out and tell the truth. Clearly, he thinks there's something wrong with him. But he also thinks there's something wrong with "us," namely, his family. This is a family which believes that Erik can do no wrong, and which therefore tacitly encourages Paul not to reveal the unpleasant truth about what his big brother's really like. Paul's silence is his family's silence.