Um…so wait…does this mean that one should never invite shabbos guests, or should only invite female shabbos guests? Because otherwise someone’s wife will be cooking/baking for someone else’s husband. I don’t see how a shabbos meal should be any different than a plate of cookies. In fact a shabbos meal is perhaps more intimate because the wife may be directly serving the other husband.
Never is a very unforgiving word. Yes, though, mixed couple socializing can be dangerous and in many cases should be avoided.