If that possibility is too much of a concern, maybe we need to come up with an alternative - like some kind of decentralised, mass-distributed reddit-like. Actually, wasn't that usenet? Is it too late to get that back?
Invisibly editing comments is a very unexpected route to take. I doubt you could push most CEOs to that. They would just delete the comment.
That you'd say this is an indication of how far the culture online has fallen. What's now taken as an accepted use of moderation power was once considered abusive.
We all know that site operators can change things, but some of them have enough integrity to be trusted not to.
And you know this how, exactly? Because the perpetrator said so?
I find the scenario that this was the first and only time this was done implausible.
[1] Modifying Reddit software to let them hide the edit from the comment author would be visible to anyone with source access, meaning it can't be done without the support of all of their developers, and so probably wasn't.