[edanm]

What about childbirth? Do you think that we weren't designed to have children?

I think you're mixing up a few things here. The reason things hurt is because you are doing physically demanding things with your body. Evolution can't just make something which takes a lot of energy not take that energy. It could get rid of the idea of pain entirely, but that's bad for a lot of other reasons.

That's like asking why our bodies were even designed to get food in the first place instead of not needing it. There are physical constraints involved.