Many of the Catholic Church's problems stem from the fact that members of the clergy are in positions of authority and trust which can be abused to gain access to small children, one key reason that these positions were abused in a way that would never happen to, say, a company full of actuaries. A Mars mission wouldn't have this problem. It also has much smaller staffing needs, at least for the time being.
Screw this. I take back my earlier remark because I think I've just uncovered the real reason that sex will be a major problem on a Mars mission: it'll be run by a government bureaucracy in a society which cannot talk about them rationally on either side of the topic. It'll be a culture-war thing and the Right will demand vows of eternal chastity not just for the crew but for the rocket technicians as well, while the Left will demand strict polyamorous relationships for all astronauts just to spite the Christians.
society. y'all are all inane
Let's try it. I'll not have sex for a month and you won't eat or drink for a month.
That is my point / argument. You may disagree, but I'm not gonna listen much unless provide some evidence.
You may indeed be able to find a dozen people that claim to be willing to abstain from sex for the rest of their lives. You might even find a dozen fervent believers whose religions are sufficiently compatible that they don't kill each other before the end of the mission. But if you put them in a box for the rest of their lives, I would not bet that these vows of chastity will hold. And what then? Punishment? Voted off the space station for having sex? This sounds like a recipe for repression on a level that would impress the Saudis.
The Catholic Church can't even reliably enforce chastity among its professional clergy. I don't think this issue can be waved away.