The intent is not to avoid sex but to avoid procreation.
Better, and wiser, to put infant supplies on board.
We won’t be sending humans to Mars. The human body is continuously shedding various microbes, not to mention bodily waste. We won’t risk contamination of Mars, especially after it’s confirmed there are existing life forms on Mars. So we’ll just keep sending sterilized robots.
Humans can’t live on Mars in any case. The human body won’t thrive or remain healthy in a low-gravity environment over a long term.