facebook is not a bad idea.
It's a bad idea to put a vulnerable person in front of a PC, especially one connected to the internet.
There are things everywhere in life that are "bad", dog poo, broken glass, plug sockets, etc etc, but they still exist.
Control needs to be put into place to make sure these things do not have a negative effect on someone, especially children.
The same care should be taken with regards to social networking.
The social networking site is not the problem, its the parenting skills, or lack of them.
Don't you need to be a certain age to use it?
Also, what do you mean by bad?
facebook is great, i use it every single day, and i use it to keep in touch with my friends, family, and colleagues.
I enjoy sharing pictures, videos, and status updates of the trials and tribulations that i encounter in my everyday life, and people enjoy reading or watching them.