L4D is a multiplayer game. I can't imagine playing it alone, and I don't see why anyone would.
Because the AI bots you play with in single-player are both smarter and more skilled than any real people you will encounter online.
The 10 year olds that populate the L4D servers have no concept of team-based gameplay.
Hypocrisy is pretending to have values or beliefs that you don't have.
And I HATE people who think the game is somehow zombie canon.
The room cost $25, they paid $30, were refunded $5, each got $1 back, room service keeps $2.
Don't worry about fluctuations in the number of subscribers--mine goes up and then goes down and goes up and goes down.