A forgery is an unauthorized reproduction that is created for fraudulent purposes.
A proxy signature (clubhouse / secretarial) is an authorized reproduction that emanated from a source known by the intended signer.
With autograph collecting, there should be a clear distinction between forgery and proxy and they should not be used interchangeably.
Some collectors argue they are one and the same. Perhaps they both have an equivalent level of desirability to some (zero), but that does not make them the same.
From a personal perspective, if there was an multi-signed item that had a proxy signature mixed in with a group of authentics, it is an item I would not necessarily rule out for my collection. However, a forgery mixed in with authentic items would be totally undesirable in my opinion.