"Protestants are united in belief on the essentials of the gospel message."
Do you see anything there which would indicate "infallible" or "required" doctrine? While I may not have worded it exactly the same as Quester it is clear he used the qualifier "essentials of the gospel message". In your haste to find a "gotcha" you took a leap beyond logic.
I pinged nate on the other thread to find out what non-Catholic definition he prefers to use. And one exception does indeed disprove the rule.
An exception to what? A generalization?
Is baptism symbolic or efficacious? That is an essential. Is Christ present in communion? That is essential. Did Christ die for all men or some preordained men. That is essential.
Or have you redefined the word "essential"? Talk about a leap beyond logic to arrive at a "gotcha" conclusion.