I agree with @Gilles of course: random italic and bold text is bad. Reject edits diligently, please :-). On a more general note:
For some reason even the markdown help speaks of italic and bold. However, the Stack Exchange engine knows better, and translates this nicely to <em>phasized
and <strong>ly emphasized
.
Emphasis is meant to make something stand out in a post, thus improving readability of the post. Removing- and especially adding emphasis to someone else's post seems hard, but is in many cases very reasonable... and in many it's not. I trust those with enough rep and powers to (dis)approve edits, using their (in this case probably often subjective) judgement wisely to reject or approve on a case by case basis.
Suggestion: Having said that, it would be nice if the markdown help mentions that italics and bold translate to certain levels of emphasis, and are meant for just that: emphasis.