Why do you think you have a valid perspective?Why indeed.
The comment was actually more reasonable than the title sounds. Their point was that it's not enough to go around saying My point is valid! Listen to me! In fact most people would be included to discount anything after that.
Here's the problem with the professional left blogs: they're predicated on the notion that complaining as end in itself is a perfectly valid aim. It isn't. Negativity is contagious. Positivity can be as well, but that's another story. The act of creation takes a great deal more energy and effort than the act of destruction.
The threads at these blogs are destructive. They shed no light on the problems we face. It's an excuse to bitch and moan. And, it's destructive.