Why don't I speak with a lisp?

This old fairy tale about Spaniards "talking with a lisp" is starting to get on my nerves. Spaniards DO NOT talk with a lisp. They pronounce the letter "z" and, in some cirstances, the letter "c" like English "th" in "thick" or "thin"; but they pronounce "s" as "s"; this is not a lips. A lisp is when you pronounce an "s" sound as "th". English speakers pronounce "th" the way they do, but they also pronounce the letter "s" as an "s". No one says English speakers "speak with a lisp".