Suppose it's not community wiki?
As stated by the FAQ: Once you have 2000 rep, you can edit other people's posts.
EDIT: or if you are a moderator.
(I am assuming this is a 'moral' question and not a 'technical' question.)
And I've done it before.
Example: Correcting someone's code so that it at least compiles, etc. Not in the heat of the responses, but I came along weeks later and the answer answered my own question, co I copied the code. It did not work, lacked private modifiers, etc. So I fixed it.
This is all in the spirit of SO.
There is a line where one could go to far, like trivial edits, which is a full on topic here on MSO.