It depends on what you are calling sex. If it is based on penetration, then kids are aware of the risks, and women have been stepping up and saying please do better or else ... No
Birth rate is critical for most of the progressive entitlements sure, so that will be a down side people will need to figure out, but it isn't a world ending situation.
The reality is building the connection to have really great intimacy based sex means no stress for both women and men. Our society living hand to mouth is so not conducive to this. Want upticks? We need subsidized day care and a program akin to veterans who get called in for war. That is you have a child both parents stay at home and their full pay is covered by the government.
People might not worry so much and may enjoy sex.