I think that there is a distinction to be made within MO that is not being made here.
There is the group that is using “its ok, I’m MO” as an excuse to be mekil/ over aveiros, bordering on Conservative, except being more widely accepted. But the other group, often called YU Machmir or Torah Umaadah is the group that is MO while still holding (mostly) to Halacha. The ones that do send their kids to non-co-ed schools, dont go mixed swimming,the mothers cover their hairs and wear skirts, some even wear tights. the fathers go to minyan 3x a day and have a chevrusa or 2 every day while doing daf yomi, etc. They are MO because they believe in Torah Umaddah, as a way of bringing them closer to Torah, following The Rav (r’ solevetchik as he is called in those camps).
so the MO bashing on a wide level has got to stop.
(and no, I am not saying this b/c I am MO, but I grew up in a house that was that second type of MO, going to schools of the first type, and very much saw the difference. Yet I still became Yeshivish)
also, regarding what charliehall said that ” Rav Soloveitchik z’tz’l, who qualified as a Gedol HaDor, was an enthusiastic supporter of co-ed schools, founding one himself in Boston”. I think if you read the Teshuva thoroughly it implies that he did not see it as a lechatchila, but rather as a bdieved because this was the only way that the MO parents in Boston would send their kids to his school instead of the secular prep schools. And you can’t say that the fact that he allows it shows that he’s more modern because Rav Moshe, who even you can not deny was a Gadol Hador also has a teshuva about until what age Co-ed education is OK, and under what circumstances.