>It strikes me that apart from the married/unmarried female thing it's only purpose is to lend a polite form of address by not using a person's first name.

The whole caper could be dispensed with by simply considering it polite to address people by their given names.<

From your stories, it seems as if there is more offense and confusion generated from the use of Mrs/Miss/Ms than there would be in dispensing with them. Here's to the scrapheap! (and less boxes to fill in on forms)