I learned long ago, and keep it clearly in my mind, that what AV considers "malware" and what the user considers malware are not entirely the same.

and if clearly false could be used in court.

I do wonder if Windows becoming adware, but then the built-in antimalware detecting possible "competitors'" adware and removing it, could be challenged in court as anticompetitive behaviour.

You, personally, can turn off Windows Defender, but your users probably have no idea why the app they're trying to run doesn't work when they double click it. They're also probably shown multiple scary warnings that discourage them from using the app and trick them into thinking it's broken or malicious.

It's a hurdle just to convince users such an app isn't malware, and then it's an entirely other hurdle to help them actually run the software by bypassing Defender.