Some who argue against the autohoax critique of media will use "I don't know because I wasn't there" to undermine the skeptics’ confidence that the event in question was faked. The implication is that “we,” the non-media, weren’t there. Therefore, we can’t know if it was fake.
This is a cop-out.
To say that nothing is knowable or real unless one can personally and physically attest to it presents an unreasonable burden of proof and is tantamount to reality denialism.
Distrusting liars is not denialism of reality but a defense of it. We know something has happened, but we differ in its meaning. Simply stating that one "does not know" presents a void: what is the default assumption behind their "I don't know"? Are they suggesting that the event is to be assumed real since they weren't there?
We need not be physically present at an event to know it happened. Regarding news events, autohoaxers do not suggest that the event did not happen but that the reportage is deliberately misleading by design.
It is up to the individual news consumer to decide where they place the burden of proof. If one trusts the media and accepts the claims at face value, then the default is that each story is true unless stated otherwise. Ironically, this means the only time you would know you've been lied to is when the liars decide to report on their own lies. (Note: they may do so occasionally but only to make a scandal of it and give the impression that lies are an exception to the rule and are punished and not rewarded.)
The faithful adherents to the church of MSM trust the media and accept the burden of proof. Their major flaw is in assuming the media are eyewitnesses and that reporters are recording reality in good faith.
Those rejecting the screen's implicit argument from authority may only claim to know an event has been reported but do not assume the reporters are mere eyewitnesses with cameras and microphones, but understand news media’s role in a worldwide and monolithic psychological operation.
Autohoaxing is an informed agnosticism. Rejecting claims is not the same as denying reality. Believing the news as the truth by default results in a lie-augmented reality. Consider how easy it is to list the things that do not exist yet still enjoy widespread popular belief.
The default belief system proffered by mass media places tuned-in believers in a highly subjective universe, but they don’t notice because they are trained not to doubt what they are told from their chosen sources.
Skeptical non-believers, by contrast, maintain a reality-oriented perspective characterized by standing on what they know. They recognize the highly mediated opinions approved for the massified mind but do not accept them as valid.
In summary, the only rational follow-up to "I wasn't there, so I don't know" would go something like this:
"I don't know either, but my default position is fake until proven real, given that all mass media propaganda events occur in the context of a ubiquitous but covert psychological warfare campaign."

Humans approach understanding reality ONLY through theory based on congruent evidence in my view. That is the worldview based on the scientific method.
And, yes, experience shows liars are likely to have a pattern of lying for on-going covert goals. The MSM, especially when promoting themes and agendas judged prior to be strategies for ruling class tyranny and oppression, should always be suspect for such lying. Based on experience we can also suspect some resistance the covert agenda to be undermined by self-defeating ideas concocted by the same ruling class and transmitted by MSM.
Jumping to the conclusion that all resistance is controlled is a mistake. The resistance (or reaction) to the ruling class agenda is very diverse and natural, but often partially informed by non-scientific attitudes. Much can be doubted for lack of evidence. But, it is a mistake to autohoax the resistance without specific discernment.
My fallback is to reminder the auto believer that WMDs never existed and was a total lie. No one still thinks WMDs were/are true and that usually wakes people up out of their stupor.