Here's the truth folks... When you read someone's LiveJournal (or any blog for that matter), you're getting a very, very single-sided perspective of things. It's what they think, from their viewpoint, and how they feel about it at a very specific moment in time, with only the points that substantiate their argument. There are probably a lot of opinions that would contradict the blogger's viewpoint. There are probably a lot of things that might redeem someone they're speaking negatively of. There are probably circumstances that they're not even aware of that would render their rant completely baseless and/or prevent them from writing it at all, if they knew. (Ironically, these concepts all hold potentially true for this rant as well... go figure).
That being said, when you see someone that you've read about in someone else's LiveJournal, take it with a grain of salt. The issues the LJer talked about or were frustrated with may very well have passed. Things may be warm, fuzzy, and peachy in everyone's world and you're just not up to speed. Curious? Fine... there are very practical, socially acceptable ways for you to find out what's going on without saying things like "So-n-so said some really bad things about you in their journal" or "I'm surprised you and so-n-so are talking, with the kind of person they made you out to be in their journal."
Maybe it makes you feel like you're in-the-know to demonstrate how informed you are by saying such things. Maybe it makes you feel good about the banality of your own life to stir up trouble in the lives of others. Maybe you're simply socially inept. In any case, it makes it look like you're out to stir up trouble... create drama... be an ASSHOLE. Especially when it's in a very public place.