There are at least two types of people who make negatives comments.
1. First, those who are disgruntled with wherever or whatever there are in life. The person who didn't get his or her dream or at least a satisfactory job in their dream or a satisfactory location, or had to settle for a specialty they only sort of liked, or has always just gone thru life with a chip on their shoulder or a scowl on their face, etc. These are the whiners, complainers. It's unlikely they'll ever be happy no matter what they do or where they go. And they'll just take it out on whoever will listen to them...including SDN where they can anonymously whinge. Everyone else should serve as their dumping ground. These are the people you can't reason with because they'll always find a reason to disbelieve your reason.
2. But then there are also those who are otherwise content in life. People of sound mind. Mentally and emotionally stable. They have little to gain from voicing negativity let alone voicing negativity online. Yet they truly believe the negativity is reality or is becoming reality, and so perhaps to inform, or warn others, or perhaps simply for love of a specialty they see dying, they tell others what they think is the truth. They wish things weren't so, and would be the first to admit they're wrong if it turns out what they see doesn't come to pass, and they respond to counter arguments rather than letting emotionally charged adjectives alone do the heavy lifting for them.
I believe people like Blade and FFP would be in the latter camp.