I can identify one significant problem with a mixed sex crew complement in a multi-crew environment, and that is that if a crew member finds a mixed crew to be a problem to himself or herself, they should consider work elsewhere. If they wish to keep flying, perhaps single pilot operations might be a suitable alternative.
The same thoughts extend to differing sexual preferences, race, religion, etc. in the cockpit.
It's an entirely different issue if a mixed crew results in under qualified people being awarded jobs pursuant to filling a politically correct "quota", or national pride puts similarly under qualified nationals in the cockpit to "balance" the numbers with expatriate crew.
Regards,
Old Smokey