The ability (and the need) to edit other people's words is a sign of power over them, especially when it can be done without leaving a trace.
The WELL, one of the ur-communities online, has this bold fundamental statement of literary authority:
You own your own words. This means that you are responsible for the words that you post on the WELL and that reproduction of those words without your permission in any medium outside of the WELL's conferencing system may be challenged by you, the author.
By posting a comment on Politonomist.com, you grant Politonomist and it’s subsidiaries an indefinite and unlimited license to reproduce, edit and make use of the comment in any non-slanderous method seen fit.
At least they said "non-slanderous".
One of the fundamental reasons that I continue to write on my own weblog as opposed to transferring my digital identity to some other system is that I have edit rights on all of the content and all of the discontent here. If someone publishes a comment, I have the ability to modify, delete, and quote from it. I'm not certain that I've asserted any specific moral rights to do this, but practically the "edit" button is all you need.
Oh, to be writing in a place where word ownership was unambiguous.