I don't have any issues sparring with women. I hold back and they usually go full throttle but as suggested there is a big difference between sparring and fighting someone in the cage where a man would likely find himself in a catch 22 scenario.
If he loses he shouldn't have lost to a woman if he beats the shit out of her people will be quite disgusted. Either way you leave the cage feeling like shit and looking like a complete asshole.
Best Fighter on the planet.