BF has been riding A LOT since he was about 10 years old and, after 20 years of such treatment, we don't suffer from any dysfunction in this area.

This being said, I do believe that a bad fit and prolonged pressure caused by some positions on the bike (like leaning in the aerobars) could have a numbing effect if the saddle and fit are not right.

I've also had a friend complain of pain and severe numbness in the genital area, presumably caused by a non-fitting saddle. He's an ultra-distance triathlete, and shopping for a new saddle. Last I heard, he got a new one, and stayed on it for just 10 minutes, "I'm careful you know!"