Depending what I was commenting about... I may want to stay anonymous. If it was to protect myself from retaliation especially. Certain things that could be said... depending on who/what... could be dangerous. Job loss, friendships lost, etc. I would even imagine vandalism could be a risk depending what it was.
It's a thin line... I can see where it is basically gossip. But it also could be a way to get the word out. To get others thinking. Without risking your own well being.