Q:

Should I rollback a user's own edit? 

The OP of this rock identification question vandalized his own question in a fit of pique.  
I flagged the question for deletion, but then I thought maybe just rolling back the edit might be a better idea.  Then it would go back to a perfectly normal, garden-variety (inadequate) rock identification question. 

A:

Yes, please rollback edits that vandalize a user's own post.  This is a little more important when the post is relevant/on-topic, but the same rule should generally apply everywhere.  By rolling back the edit, we prevent nasty non-Q&A content from being on the site, while either keeping good-quality content or (in the case of poor-quality content) preserving the post so the user or someone else could possibly improve it.