It's not about it being acceptable. But Khan is the bad guy and does bad things, including crushing people's heads until they pop like a grape that's been stepped on. It's how we know he's the bad guy.
But I think audiences would've been a bit more squeamish if if was a woman in that position. Especially when domestic violence is still a real issue and tough to crack.
Khan was the ultimate sexist in 'Space Seed'. He actually committed domestic violence against Marla McGivers.