When people communicate online, it's difficult or us to get a clear picture of who they really are as human beings. It doesn't mean they aren't being genuine, but we tend to base a lot of our impressions of others on; their tone, the look on their face when they say or do something, how they react to specific situations, etc. And, these are extremely difficult to decipher online (if not impossible).
Still, it seems that it's in our nature to need to come to some kind of conclusion regarding who/what people are.
It's true that some people are not honest about who they are. This can be said of some people in real life, as well as online. Certainly, though, there are plenty of people who are perfectly honest about the people they are and can still give one the "wrong" impression.
I've actually had at least one person, online, think that I'm some sort of hippie that farts rainbows and sunshine everywhere she goes. "Funny" doesn't even begin to describe that reaction to who I am, from my perspective (as well as from the perspective of anybody who's taken the time to get to know me).
Don't get me wrong, there is nothing bad with being the kind of person who does do that, IF that really is who you are (although, I would feel compelled to assume you're taking some REALLY good anti-depressants or something).
Most people though, myself included, are complex critters. We laugh, we cry, we scream, we rage, we joke or take things far too seriously, we hurt, we hurt others, and so on. Like mood rings, what color we show depends on the situation, our mood, and a variety of other factors.
A person who is truly genuine about their whole self can easily be kind one minute and cruel the next, all depending on the circumstances. That doesn't mean they are being two-faced, it usually means that they are simply being honest about their reactions - not hiding behind a computer screen or trying to "keep the peace" by lying to you about how something makes them feel.
I don't trust someone who is always the same; who always, regardless of circumstance, wears the exact same mask. I appreciate people who are honest about their feelings, their struggles, their strengths and weaknesses, etc. I find them more well-rounded, more full of life, more genuine.
I'm not saying that the feelings of others shouldn't be taken into account, or that there aren't times when perhaps something could or should be sugar-coated. Sometimes, depending on the situation, that may be the diplomatic solution, or the only way to ensure that your point is heard or understood.
Still - I'm not a fan of anal smoke-blowing.
I'm one of those who likes BRUTAL honesty. I want people to say exactly what they mean and mean EXACTLY what they say. No, my reaction may not always be peace and love, but I'll respect you more for your complete disregard for whether or not something you say will upset me in any way. I'll respect you more for being entirely upfront about who you are, what you believe, what you think... And, in the end, we're more likely to become good friends.