Ha! It's more than contraception availability although that certainly is why I qualified my bafflement as being in regards to reasonably intelligent people. It's pretty easy to imagine how this could happen due to temporary or permanent affliction by idiocy.

None of the personal examples I have in mind had circumstances that explain the resentment these men expressed. I think you're right that they simply failed to anticipate how parenthood would be, or maybe they didn't even recognize it as something worth consideration.