i'm guilty of it.
i really try to follow the mantra; if you dont have anything nice to say, dont say anything at all. this has worked for my parents generation and has served them well. i have been known to drop the ball. i know this.
i think the anonymity of the internet has taken that thought process, put it into a bucket, and we all crapped into it and lit it on fire.
if you did this in real life, face to face, i don't think you would develop any deep meaningful friendships.
take the ubiquitous, "Should i buy this Chevy Truck" thread (insert any truck, really). there is no GD way that will end well on a forum. (especially if it is a Ford Forum). i've seen it happen here on one of the friendlier forums. PPOT.
i think on the internet, we all have some sick facination of watching each other, hoping we fail so we can say, "i told you so".
it is a weird dynamic.