From http://en.wikipedia.org/wiki/Mr._Snuffleupagus:
In an interview on a Canadian telethon that was hosted by Bob McGrath, Snuffy's performer, Martin P. Robinson, revealed that Snuffy was finally introduced to the main human cast mainly due to a string of high profile and sometimes graphic stories of pedophilia and sexual abuse of children that had been aired on shows such as 60 Minutes and 20/20. The writers felt that by having the adults refuse to believe Big Bird despite the fact that he was telling the truth, they were scaring children into thinking that their parents would not believe them if they had been sexually abused and that they would just be better off remaining silent.
