I would rather get rid of eating but keep defecation, though I don't know that I could say why. The relief/satisfaction thing is certainly interesting.

I once had a conversation in this vein that went like this:

• Him: In Heaven, pizza grows on trees.
• Me: In heaven, people wouldn't need to eat.
• Him: Good point. But maybe eating as a form of pleasure?
• Me: kinda flabberghasted

If nothing else, the parent got me to evaluate my preferences and realize that I was using them hypocritically in situations such as the above.