ughhhh you don't get it. stimulation only occurs when you apply pressure. the skin outside of that "pleasure" doesn't add to the pleasure its just skin. the nerve endings for skin are different then those that are inside. try it on yourself. try touching only the skin and then apply pressure to the underside of your dick. you will see that the "pleasure" comes from the inside. when foreskin is there. the skin on the outside does not protect the sensitivity of what on the inside

also in that eye analogy you'd still be able to see just like you'll still be able to have pleasure with no foreskin