I was a mod on a site once (actually still am, which is why I've said in the past that I really really really don't want to be a mod at any other site... the job bites.. ok, there are other reasons, but that's the most relavent), and the golden rule there was close threads if you must or if you had to delete make sure to tell the poster why.
The reason was because otherwise people would complain about "abuse of power" and/or misunderstandings and hurt feelings would occur.
Hmmm.
Hmmm.
Hmmm.
Being a moderator does suck, it's a tireless, thankless job... but it gets harder when you strong arm it as someone who is upset about something is less likely to act in a rational or reasonable manner... and more likely to take it personally (which it rarely is)
The best motto for a mod: Be nice, until it's time to not be nice. (and even then handle that part in private)
Edited: additional thoughts