You will always need an Egg or Sperm depending on which is missing in the relationship. Also, one of the parents would not have genetic code in the offspring since you can't splice two eggs/sperm together as far as I know.

The demographic trends we're seeing now (declining birth rates for affluent people in the developed world) could be due to our natalism level being mis-calibrated for our current circumstances.

It's good evolutionary strategy to reduce the birth rate to compensate for successful reproduction (i.e. more pregnancies that result in offspring that reach child-rearing age themselves), as otherwise populations will explode beyond the carrying capacity of the environment (or pay more of the fixed resource costs of raising children than is necessary).

What we see now, however, is that in situations where both pre-adult and maternal mortality rates are exceedingly low (such as has been the case for the last ~4-5 generations in the developed world), the strategy undershoots the replacement rate.