I believe it to be a part of a societal trend of many men wanting to "defeminize" women and consider them to be basically the same as men and thus not worthy of any special regard or respect.
[Sickbay - medical ward] (Khan is lounging, showing off his chest and calves.) MARLA: Ship's historian, Lieutenant KHAN: Marla McGivers. MARLA: Yes. KHAN: I am told you participated in my rebirth. MARLA: In a small way. KHAN: I've been reading up on starships, but they have one luxury not mentioned in the manuals. MARLA: I don't understand. KHAN: A beautiful woman. My name is Khan. Please sit and entertain me. (She perches on another bed) MARLA: I'd like some historical information about your ship, its purpose and KHAN: And why do you wear your hair in such an uncomplimentary fashion? MARLA: It's comfortable. KHAN: But it's not attractive. (He takes her to a mirror and loosens a couple of strands at the back.) There. Soft. Natural. Simple. MARLA: Mister Khan, I'm here on business. KHAN: You find no pleasure here? MARLA: My interest is scientific. Men of. That is, the world of the past. I'm sure you understand to actually talk to a man of your century KHAN: There. Simple, soft. Please remember. MARLA: Perhaps some other time, when you feel more like talking about the past. KHAN: I'm glad you came. Please do it again.
Or it's just short hair. There have been many periods in human history and culture when long hair was considered manly.
In 2017, a woman with short hair is not masculine, but she is more likely to be progressive and independent, in my anecdotal experience. I go for these women most definitely. I have a neck/shoulders fetish so short hair facilitates that too. For Dayton, it means she might hit back, which is too great a risk.
On a vessel that expects to encounter hostile forces, short hair makes sense as it makes it harder for an opponent to grab it during combat. Also, I believe that the main protagonist of this story was raised on Vulcan, and both Vulcan males and females generally have short hair (although there are exceptions).
I think Dayton finds it sexually confusing. He is not sure if he should be attracted to women with short hair. Maybe it triggers some latent homosexuality which he tries to repress with religion?
Maybe the poor fella just doesn't have proper facial and anatomical identity scanners in his brain. I can recognize women if they're bald, if they're done up as men in man-drag, I can tell a girl hand from a man hand, a girl foot from a man foot, etc. I think most of us could. But if your scanner is broken, shit, I guess you would need blatant neon signs to keep your dick from going in the wrong hole. I bet that would be a terrifying world to walk through. And then to on top of that be STUPID? A person like that would get a bit cranky, I wager, and wonder why nobody is helping them out. They'd probably get all tinfoil hatty after awhile. Poor bastards. I wish I knew how to help them. Oh, wait, here's an idea, accept that you can't fuck everybody, and learn to appreciate people as human beings for their talents, and skills, and personalities.
Women's hair length doesn't annoy me. The moronic ruination of the Klingons though... I mean... how the fuck was B'elanna's dad supposed to find one of those insectoid looking things attractive. Yeah, that relationship should never have happened if we're supposed to believe that this is how they all "really" looked. It's especially dumb since Enterprise already gave a good explanation for why the TOS and TNG/DS9/VOY Klingons look different. The TNG/DS9/VOY appearance is their true appearance. The TOS appearance is an abberation caused by pretty much the entire Klingon species being infected with human augment DNA. This was eventually weeded out by the time of TNG, resulting in them getting their original apperance back. But this stupidity on Discovery... The only possible fix for this is if some later ST show retcons it and says that these are not actually Klingon Klingons, rather they are auxiliaries of some other conquered species serving within the Klingon military.
I figure B'ellana's dad was double dog dared to do the deed as a fraternity hazing... and her mom was in the sorority
Point of order, in TWoK, Saavik steps into the turbolift with her hair down to her shoulders, Kirk looks at her and says, "Did you change your hair?" Saavik responds with, "It's still regulation." Starfleet, it seems, doesn't prohibit women with long hair.
Women can have longish hair in the US military but they have to put it in a bun or otherwise control it while on duty. One of my female coworkers is a Navy reservist and her hair is about shoulder length.