I don't think they assumed they could not do it as much as I think it was because at that time in history, men protected everyone else and no man would ever put a woman in harms way. Sitting on a rocket / slow exploding bomb was on the dangerous side as is space, reentry and landing.

Could you imagine being a single man on a spaceship with a single woman for a whole year? The periods causing the mood swings. The questions she would ask. The nagging reminders she would make at you. The accusations she would make at you if you said something that did not align with her bogus ideations of feminism. Men became pussies in the last 35 years. The fact they let women into anything we do is a fucking joke.

Thank heaven they let women start being rocket jockeys. Remember that well-adjusted genius who drove cross-country in one of her space diapers so she could go after her lover?