Just because I feel like being a devils advocate here is a position I recently flipped on with reasoning.
1-Logistics
Unless you go star-ship troopers style (which creates MASSIVE legal liability issues for any claimed problem) you have to double up on a lot of things. You need double the sleeping quarters, toilets, showers and a significant increase in medical care in order to accommodate women into any pediment base.
2-Buffalo
Just like buffalo males generally circle and protect females when danger comes around. I cant say what it was off the top of my head but this has been tested over and over and generally speaking guys become more interested in keeping the females in their unit alive than in accomplishing their mission
3-Biggots
I think it was the Scandinavian army that was so low on troops they brought women in. One issue they had was that they were fighting traditional muslims and those guys would rather fight to the death than surrender to a woman. This meant that instead of an enemy giving up they would just keep fighting until their last breath which resulted in more casualties.
4-Emo Kids
Guys just psychologically respond different to a girl dying than a guy dying. When their friend dies they get fucking pissed and want to murder the enemy. When a girl dies they get depressed. Its 10 times worse when they are cleaning up the body parts of some person they wanted to fuck. That shit will make any bad-ass killer emo as fuck
5-Physiology/Mental state
Guys can lift more and push harder. Its genetics. There are totally exceptions. I'm sure there are tons of bad ass girls out there that could kick my ass but in general- anatomy is a fucking thing. Set aside physical limitations and emotionally women just have more needs. Low maintenance is a total necessity to be a soldier and some needs just can't be addressed.
So can a girl function in a combat role? Sure. But her being a girl will increase logistical obligations, cause the enemy to kill more of ours, cause more issues with fellow soldiers if she dies, distract from mission objectives, and require a girl thats capable of throwing as much weight on her back as any guy next to her while squatting down and shitting in a bottle next to a bunch of guys. Even if she was the perfect bad-ass because guys are flawed integrating women into combat roles only hurts productivity, cost, and moral. Objectively it will also have an impact on effectiveness in multiple ways even if those factors are ignored.