I could buy into the political correctness explanation if this were a recent phenomenon, but it isn't. This is something deeply ingrained in our culture, and has been probably since the Pilgrims came and kicked out the Native Americans.
Following that line, times were tough in the 1600, 1700 and 1800s. People worked hard to clear the land, plant the crops, harvest and preserve the food. A daughter that could do the hard labor expected of a son would be a blessing. A son who only wanted to cook, clean, sew, and pursue the "womanly arts" instead of chopping, hunting and plowing was more likely to be forced into the "manly" role. This is not to take anything away from our women ancestors...their work was every bit as back-breaking and tedious, though generally less physical strength was required.
Scary...but as I wrote that, it had a ring of truth...
Also true that the Aristocrats of that time had more leisure (as they had servants and/or slaves to do the hard work) and were probably considered effeminate and useless by their poorer and harder working contemporaries. Does this mean that the cultural distaste of boys acting feminine was really rooted in Class warfare? I guess maybe if you use a conspiracy-theory type of logic.
Anyway...there are some more thoughts...please feel free to shoot holes in this
.......Laurie