In fact, I myself have seen no problem with having a few select Infantry units be "co-ed". I can even see some real advantages to having a few such units, using them for example as Israel does. Mostly as defensive units, where having females as part of a defensive force could even help ease tensions in areas of the world where sexual segregation is high.
But simply throwing open the doors into all units? Nope, I see absolutely nothing to gain from doing that. However, after creating a few such units and then tracking key information for a decade or so, I also am more then willing to look into it again and revise my opinion.
The thing is, we already pretty much
have this, and we have had it for years. The Military Police are co-ed, and they've long been tasked with "defensive" as well as "peace keeping" missions. If you're looking to capture "hearts and minds," MOS types like PSY-OPs, Linguistics, Public Affairs, Intel, and etca are all co-ed as well. It's simple enough to just temporarily attach one of those women to a more combat ready unit if the need presents itself.
Unfortunately, that logic won't prevail here, because what the Left is chasing isn't anything practical. Rather, it's some mythical vision of "GI Jane," inspired by "GUUURRRLLL POWER!!!" flights of ideological fancy. I hate to be the one to tell them, but the simple fact of the matter is that what they're looking for just doesn't exist in reality.
There might very well be a small handful of "1 in a 100 million" statistical anomalies out there who can kinda/sorta fit the bill. However, that's not enough to justify changing the entire way we do things, especially not when - as you say - the resource cost of finding and acquiring such persons will undoubtedly be through the roof, and we could simply recruit a man who would perform just as well, if not better, for a small fraction of the cost instead.
For that exact reason, the more likely scenario here isn't that they will search for women who can truly "hack it." The most likely scenario is that the powers that be will simply lower standards - either just for women, or maybe even for men as well as women - in order to make sure that even more average sorts of females, who would not normally be qualified, can get in. That's going to be a disaster.
We'll either - assuming that standards are lowered only for women - wind up with frontline combat units handicapped by having under-qualified female Soldiers dragging everyone else down, if they're not simply knocked out of commission by the physical strain of training and operations. Or - if they lower the standard for both sexes - we'll wind up with combat units full of slack fat-bodies who can't compete to the performance standards of our enemies, and are
still handicapped by women performing to an even lower average standard than that.
Either way, it's just an all around
bad ***ing idea.