It's bad for reddit, but it isn't some kind of injustice against speech.

>Can their users (and consumers of their ads) trust that posts aren't being doctored?

So far one post has been doctored that we know of out of millions (billions?) of posts on the site, so reasonably, yes you can.

But the next post you read could be the 2nd-in-a-billion(s). I could see this behavior from a "mod" who had such capability or a rogue employee with database access, but the CEO personally??

Where does it end? What threshold must be crossed until it can't be trusted? Who knows how many times it's been done. He got caught ONCE. Who knows how many OLD posts have since been slightly altered for FUTURE visitors who weren't there to see the original?

A vast majority don't post, don't track a single user from one thread to another, and don't even both voting. Why would they care if the post is being doctored? Or the comments, for that matter?