It would therefore be just as good to perfect in him the organ that he had, as to confer upon him another which he had not.

This is untrue.

No conceivable perfection of touch would reveal phenomena of light, and the longest arms must leave those phenomena undisclosed.
After recounting various other peculiarities of thought, Diderot notices that the blind man attaches slight importance to the sense of shame.

He would hardly understand the utility of clothes, for instance, except as a protection against cold.

He frankly told his philosophising visitors that he could not see why one part of the body should be covered rather than another.