I sense you're being tongue-in-cheek, but how would something like blockchain help this situation? (I genuinely don't understand -- can you walk me through how that tech would validate a video's authenticity?)

Second, it would only help to validate that a video was taken (and possibly that it was not modified? But I suspect a great deal of video footage gets modified after capture, for light balancing and whatnot.)

Beyond that, however, the problem is larger: videos can be started after a person incites another. They can selectively film parts of an incident, so you miss details off-camera. They miss context, can push an agenda -- all of which are (IMO) the bigger problems than validating a video provenance. (Also, the latter would require skepticism of all non-blockchain'd videos -- something that would take a major cultural shift.)

Decentralized reputation system that uses Proof of Stake to validate the "truthiness" of an individual. Users validate an idea/content by sharing some of their reputation to lend credibility to another.

Isn't think what PageRank is? I have a website; by linking to you, I am vouching in a public space that I believe in your truthiness?

Pages are not specific enough. We need RationalArgumentRank.

this assumes a basic level of intelligence that I really doubt we as a species possess. Don't you think the majority of red or blue tribe e-warriors would happily stake any amount of reputation on something they agree with, regardless of authenticity?