You can still get hard without balls, from what I've heard from others.
Used to have a buddy in college we called "Beans." When people would ask why we'd tell them it was because he was born without a frank, so he just had the beans part of frank and beans. Was worried at first it was too cruel and would blow up his game with the ladies, but he actually got a bunch who wanted to see for themselves, so it all worked out in the end.
but....if there was no frank, what the **** got worked out in the end?