“They” can also be singular when used in such context, but you knew that.
It is incorrect. It is a construct of the latter-day PC crowd who do not want to “offend” us women by requiring one sex or other when speaking singularly. It does not offend me to assume “he” instead of “they”.
Not in actual English. Only in Leftspeak. The adoption of Leftspeak by conservatives affects their thinking. Words and grammar are the tools by which the brain thinks about things. Turn over the design of words and grammar to the Borg and you gradually lose your ability to think outside their box. You accept their definitions and conventions when you use their shorthand.
When MSM collectively switched the politically symbolic colors, red and blue, conservatives accepted it with hardly a whimper. Now the color designations have lost their meaning altogether. The left's proud use of Red to designate the totalitarian left once told people a lot about certain groups without having to parse speech and listen to all of it to see if it added up. Bit by bit I see the conservatives on FR adopt the patterns prescribed by the Left. The omnisexual "they" is a feminist construction to keep it in our minds that there is NO difference between males and females. I suspect if you reverted to the proper use of pronouns you would feel very uncomfortable not using at least "he/she-him/her" or maybe it should be "she/he"- you don't want the ladies to think you are dissing them.