Also, the perception of certain body parts being out of proportion is only when we look at the statue at eye level. If you view it as it was intended, up on a pedestal so that you're looking UP at it, the hands and the head appear proportionate because they're compensating for perspective. IF my art history serves me correctly, there was a time when a plaster fig leaf was applied to David, at least for a visit by Queen Victoria. But the whole thing is rather ridiculous to be worrying about covering up body parts out of prudishness rather than climate-dictated need.
I think it's a vain effort to try and separate the erotic from the artistic - and there's not a damned thing wrong with having your cake and eating it too when it comes to this. I think part of the impact of a statue like the David or the Pieta is the stark, confrontational physicality and humanity of the figure being nude. David was to inspire the Florentine republic as an heroic figure who was also human. How more human can you get than when naked? And certainly the erotic charge of this virile young man, a conqueror and giant-slayer without arms or armor, would inspire anyone. The nudity of the Pieta reminds us of the ultimate humanity of Jesus - none more corporeal and human than the naked body. Seeing the form of vigorous youth laid low doubles the tragedy - someone who you can picture in a sexual way now dead magnifies the sense of tragedy. I'm certain this was a thought in Michelangelo's mind as he was creating the statue - he was a master of the psychology of art as well as its practice. If he had Jesus in a funeral shroud, we'd look at it and say, "oh, how sad for the mother. Didn't he do a beautiful job rendering fabric in marble?" instead, we look at it and immediately feel a profound tragedy. Were Jesus draped, it would be just another statue at the Vatican to be noted as stop number 23 on the tour.