I guess there could be cases where it clearly wasn't ethical, like if the ex would've gone back to her maiden name but is keeping the ex's name just to make him miserable or because there's some prestige attached to the married name...if the intent is to accrue benefits or cause pain.

Absent that, there's plenty of ethical reasons to keep one's married name after divorce, especially if someone has made their professional reputation under that name.

I couldn't WAIT to get rid of my ex's surname after my first divorce. For many, many reasons, not the least of which nobody could pronounce it.

The 2nd time, I knew I wouldn't be single very long, so didn't go back to my maiden name. I kept the ex's surname until I remarried. I wouldn't have minded keeping it forever, as my current married name, combined with my maiden name, is kind of a silly pun, but that was a deal-breaker to DH.

cm

PS: If you got a degree, etc. under a married name, you can submit paperwork to have a new diploma issued with your maiden name for $50 or so. I finally can hang up my college diploma after 30+ years.