Sex is controversial because people would like the reproduction action to be done responsibly and respectively.
We are all the result of the act, and we take comfort in knowing we are here because of intention (purpose). Out of concern, we would all like to have kids here out of our intention. Having sex just-cause means you are personally responsible for all risks. In reality, this may require help from others who did not contribute to your choice, but will suffer with you and your consequence (health, baby, etc.)