Peter really doesn't know the point of having a diary does he?
Just because he rants about something doesn't mean he's gonna go on a rampage and Grand Theft Wiley on your ass. He probably just wrote it to blow off steam. Stop worrying so much otherwise Wiley will think there is something wrong.
I'm sure if more of them said exactly what they feel about everyone they know, it'd look pretty similar. There'd be good points but they all recognize the good and bad in their friends. We're all human. Also, this seemingly meek guy surprised them by busting out a huge angry voice; did he really expect there's nothing driving that inside?
He can't just go reading people's diaries and then telling other people what he read. Unless Wiley's talking about killing himself or heavy drug use, it's none of anyone else's business.
@Manda B: Excellent point about the source of Wiley's powerful voice. He's obviously lived through some tough times, as he revealed to Peter way back. The fact that he's able to purge all of this through his singing and diary ranting, instead of doing outwardly destructive things, is actually a good way to deal with this, IMHO.
While Peter is certainly jumping the gun here, I believe it comes from a good place. I mean, he's from a small rural town where everybody pretty much knew everybody else. I assume that when anyone discovered something about someone else, the whole place knew about it right quick. Perhaps this is just his roots showing.
Furthermore, he didn't say to Michelle "Holy shit! You wouldn't believe what I read in Wiley's diary!". His first instinct was to ask if he was alright. Granted, he asked this BECAUSE of what he read, but we all know Peter wears his heart on his sleeve and can be a bit clueless at times. I guess we'll have to wait and see how Michelle rolls with it.
I really hope Michelle can keep her shit together about this. I'm going to be fucking disappointed if this goes straight down hill and she flips out at Peter without recognizing the reasons why it is completely normal, given his history, that this would occur. Sure, Peter should not have read the diary- but water under the bridge. Michelle has the opportunity to make or break this; she can help Peter understand that what Wiley is doing is natural and healthy, or she can reveal what is happening to the others, which would probably result in Wiley being alienated (and possibly lead to the tragic event hinted at earlier in the comic). Come on, Michelle...I know you have it in you, make the right choice!