They have a chip on their shoulders about it and are over-reacting, in my opinion, in the way that people do overreact when they carry such a grievance.

The primary reason the word "sons" is used in that lyric is that it's a one-syllable word which fits neatly into the line and serves the purpose admirably. The words "daughters", "children", "citizens", "people", "women" are all of 2 or more syllables, and they simply do not work as well. In the context of the anthem, the term "sons" is a generic term that simply means "the children of the nation". "Souls" or "hearts" would also work, and of recent years in fact the word "hearts" (all our hearts' command) has often been substituted.

Another factor, of course, in the use of "sons" would have been that it was normally men who served in the military at the historical time the lyric was written, not women.....but the real key is that "sons" is a one-syllable word that fits the meter and rythm and also conveys the necessary meaning (the children of the nation).

It was not intended as any deliberate exclusion of females, nor should it now be taken as such.

Be that as it may, I have no objection to people singing "all our hearts command" if that makes them feel better. I have no objection to either approach. They both work okay.