Per Debretts, it has been this way since at least the 1700s, not an “American” thing as you suggest. I’m starting to think this is just another social issue used to divide America, ie propaganda used to control people. And if it is purely preference in etiquette, what are you complaining about? The person sending the letter are allowed to exercise their etiquette preferences as well, right? Or do you also want to control people? Is this all just the fascists on the right vs the facisists on the left? This is how people like Trump rise to populisim, and how freedom and democracy die.

Absolutely not, it applies in either direction, universally. I am Mr (wife) (wife’s maiden name), this is how the language works. Why is this offensive to YOU?

It is the most correct way. Even if she didn’t take your name, and even if your not married, she is your Mrs. Not sure why this would be infuriating, it’s the language.