Maybe things were different the last time you were an editor — what, 15 years ago? — but as I understand it today, none of your stated objectives/concerns are valid reasons for editing someone else's node, even anonymous ones. (The one exception would be to close unclosed tags; and that's minor enough that it doesn't (imho) warrant an "edited by" note. Fixing actual broken markup is within scope.)

I'm sure someone will chime in that this should be seen as another reason why anonymous posting should be disabled

I'll wait until someone actually says that before I start telling them they're wasting their breath. :-)