As an employer, I agree
I run a small company (7 people) and I unlinked my employees two years ago, both from Facebook and Twitter.
While we are friendly with each other, I found myself over-analysing Facebook posts.
For example, one lady who does a good job had posted a comment to the effect of: "So bored today, why does nothing interesting happen".
At first, I was a little cross that since she'd posted this in working hours, she was clearly bored with her job. I then figured that since this was a comment on Facebook, she was basically addressing her friends, and that this is nothing more than idle conversation she might have in a bar or at a friend's home.
Employees aren't going to love every day of their job. Heck, I'm the boss, and have days where I think "why bother". It's important to give employees space, and reading their Facebook comments can be unhealthy.
Obviously there's a huge difference between "my boss is a c*nt" and "I wish my working day was more interesting".
Unlink your bosses / employees!