Yes, biologically, all life forms have/had a primary purpose of procreating. However, humans have evolved above that, we have developed brains that think and reason and we have made more of life than just eat, sleep, hunt and procreate.
If we were to stick to our "primary purpose" and the way it was originally, then we all should be self sustaining - hunt, gather and plant our food, build our own shelter, etc, etc.
We tamper with "nature" all the time. A big way we do this is with medical care and the prevention and treatment of diseases. Included in that medical care is obtaining an abortion if we do not wish to remain pregnant.
Anyone who thinks we should do what "nature" intended should turn off their computer, leave their home and go and live in the wild.