(This comment is neither a recommendation for censorship nor a push for freedom is speech)
But that type of information is only indirectly dangerous. The actual danger is the government agent or your personal actions based on misinformation in the case of antivaxx.
I was thinking more in terms of information that is objectively dangerous. Just ingesting the information alone is enough to cause damage.
I was also reminded of an article I read recently about artists and animators who worked on the newest Mortal Kombat game suffering from PTSD due to the graphic nature of their art and the reference materials they had to use.
I think there are cases for that too. But it depends on your psychology. For example there are mathematicians who have studied infinities and gone insane. Others haven't. Probably other factors involved, but it helped push them over the edge.
Alternatively, you measure how long people remember the video vividly and express the danger as the half life of the information related to it's damage.
There most certainly is. We actively codify for it in most societies in a myriad of ways. See: Nuclear technology secrets, CDC protocols, and the fact that things like PTSD exist.
And to your underlying point: stop assuming everyone is rational or will act in the best interests of society with information. There is plenty of information available to you to negate that assumption.
I think people suffering PTSD is a better example of how information can be dangerous.
Please submit some proof of this extra-ordinary claim. There is a lot of evidence to the contrary. And we're not even yet talking about whether 'Truth' is a binary value.