For some silly reason, OS X’s TextEdit app’s default format is rich text. If you prefer plain text, Defaults Write points out that you can easily set that as your default with a Terminal command.

Using CotEditor, you’ll never accidentally add formatting to a plain text file, and the app can concentrate on what it does best. This Free TextEdit Replacement Is the Mac Text Editor You’ve ...

If you keep on changing TextEdit from rich text mode to plain text each time you open the app, here's how you can change the default settings in the often-used text-editing tool.

I can get TextEdit to do this if I set "Plain Text Encoding: Opening Files:" to "UTF-8". But I'd rather not have my users make this change if not absolutely necessary (it screams support issues).