People are indeed free to express themselves, though it is not the duty of private media to enable that expression. Freedom of expression in its most basic form is for street corners. Poster here have agreed that the content may be controlled.
Sometimes I will PM a poster or thread starter to explain why I have removed a post or thread. However, that is a courtesy, not a promise, the task could be too large, or maybe I just don't want the argument. Certainly, the thread is not going to be the place where a mod will explain the deletion of a post, that will just lead to a vortex of emotion! The fact that I might PM a poster is by no means a commitment that this is PPRuNe policy, or other mods might do it, it's just me trying to be nice.
Really, my first and primary criteria in considering a post for deletion is: Would I read that post, in context, to my 14 year old daughter? If it's rude/unkind/racist etc, probably not! After a life changing accident, I easily remind myself that we contribute here to be a part of a nice group, so why not be nice!