I don't consider a cert trustworthy just because it's signed by a CA, unless that CA is mine or one run by someone I personally know and trust. I came to this position before Snowden, though.
> A signed cert has to depend on someone you dont know.
No, it doesn't. If it's signed by my own CA, then I clearly know who signed it. Likewise if it's signed by a CA run by someone else I actually know.
The point of the signing is to have someone I trust validate that the cert they signed is trustworthy even if I don't know the entity that made the cert they signed.
