How can two identical communications be perceived very differently by the same person?
Take the phrase "I love you!" and send it in two separate emails. The data is encoded and represented identically in both communications. A person reading the emails won't be able to differentiate between the emails when looking at their raw data.
Now consider the phrase "I love you!" sent to you in two separate emails: one from your significant other, and one from an unlikable business acquaintance. Both emails have only the phrase "I love you!" and no other content, but your emotional response changes dramatically once a key piece of information is known: the originator. Your initial emotional response, contextual interpretation, and even the voice you use to read the message in your head change once you can imagine who sent the message. Knowledge of origination is a key component of interpretation.
Curiously, in the long term humans tend to remember important ideas and the emotions attached to them, but rarely their trigger. Even when the information source is relevant for credibility, over time our recollection tends to reinforce concepts without retaining contextual information. The mind weakens the memories of source and eventually assumes credibility of content. Even a story you were initially unsure about in an obscure Wikipedia page soon becomes a fact "you read about somewhere" over time, and only when the information is questioned by a confident opponent does the source again become relevant in the mind.
Misinformation is spread easily because of our limited capacity to communicate publicly and our consequent inclination to trust unchallenged information. Without implicit trust we would be eternal skeptics and unable to live in a world full of assumptions that allow civilization.
More fully understanding the originator of the message when the message is interpreted yields more accurate mental context for the knowledge being stored. Politics are a clear example of how competing factions strive to discredit the candidate rather than the candidate's specifically disagreeable viewpoints. When a source is deemed untrustworthy, further communication is weakened. A source deemed trustworthy, especially one whose interpretations remain uncontested over time, has considerably more power with subsequent communication.
The ability to verify the identity of the person you are talking to, or generally speaking the source of your information, is important in all communication technologies. Advances in forgery techniques are continually met with counter-measures from governments and watchdog groups, spurred by societal pressure to utilize the full power of the network good that is an information technology. At the time of this writing it's possible spoof an email address and convincingly pretend to be another individual through text-based communication. It's not quite as easy to mimic a person's voice or visage, however, so these forms of communication have an additional element of implicit trust.
In the near future voices and faces will be easy to recreate and even fabricate from scratch. Biometrics and more detailed data regarding our identity (DNA, for example) seem the most likely next steps in the short-term, but I am uncertain how we will retain individual identity in a completely virtual environment of the future Internet. I suppose by the same token I can't assume that there will still be value in individuality for such an interconnected future. Perhaps knowing the source of communication as obviously as the content of communication is societal self-awareness.