@Russell16 Yeah, I understand your point and I think Airbnb could do a better job at explaining how the Security Deposit works.
Basically, the guest is not charged and the host is not paid for the security deposit. Why? Because to do it that way would put the responsibility for refunding the guest on the host, and let's face it, many hosts would arbitrarily decide how much to refund (charging guests for overuse of toilet paper or breaking a dish etc) or not refund at all and keep the money. Don't think that would happen? Think again...
The way Airbnb has it structured, hosts have to make a claim against the Security Deposit. If the guest agrees to the charge, fine. If they don't, Airbnb decides what's fair.
I've seen comments from guests that believe that Airbnb is totally on the host's side and comments from hosts that think Airbnb always sides with the guest. I guess they're doing a good job!