Not just the "foreskin sleeve," as you put it.
The foreskin is not just "extra skin," but it is very specialized tissue. The foreskin has about 20,000 specialized nerve endings, and the inner foreskin is mucosal in nature to retain the sensitivity/smoothness of the glans and surrounding tissues. It's what nature intended to give the male the most complete sexual experience----in both feeling and function.
Obviously the vascular and neural damage that is circumcision will diminish a male's feeling and function.
The disruption of normal sensory feedback will inhibit not only the enjoyment of sex, but control over ejaculation. And the damage from circumcision varies wildly, with the scars from the wounds located anywhere on the penis from just below the glans to 1/2 or even 2/3 of the way down the penile shaft. Because the damage is so extensive, and can be so different from one individual to the other, the resulting lack of sensory input can result in either premature ejaculation, or even the inability to ejaculate in normal sex.
Damaging a penis doesn't increase sexual ability-----that isn't so hard to comprehend.
And as far as the female is concerned, the dry, rough texture of the circumcised penis, combined with the lack of a foreskin's motion during sex is more abrasive to the vaginal walls.
Nothing good comes from circumcision, except to the unscrupulous doctors who make money from mutilating males.
Circumcision is a fraud and a hoax.
A foreskin is not a birth defect; it is a birthright.