The foundation, of course, is language. One human being can tell another more things than, say, one elephant (to take an example of an animal with a very complex brain) can tell another. But the communication dies when the speakers all die, and memory cannot recover what was said. Then came art: carvings in wood or antler or ivory, paintings on cave walls. We externalized what was in our minds so that others could see them. Not only that, but the images we made outlived their creators, so that communication could happen between persons far separated in time.
Then came writing, and with it books. Tales needed no longer to be simply memorized; now, they could be written down. And not just tales, but laws, directions, inventories. Eventually, somebody invented the library, the most famous of which was the great Library of Alexandria, an attempt to gather all the literature of the whole world in one spot. Medieval monasteries continued the collection and transmission of manuscripts. The library is like a collective brain for all of humanity. In our world today, no one person can know everything that can be known, but any person can access whatever has been known by anyone, anywhere (as long as it has been published and preserved).
Then came printing, and the costs of publication dropped dramatically. Now, more people were reading than ever, and not only books: the periodical soon appeared. Then came film, then sound recording, and radio, and finally television. The sum total of everything that could be said multiplied dramatically.
And then came the internet. Our collective mind has expanded like the early universe after the Big Bang. And since we have figured out how to keep its ever-transmitting contents from being destroyed, nothing posted online (that has been shared, anyhow) can ever really go away. We are getting into the fulfillment of what Jesus threatened, when he said, "every idle word" we spoke would be brought into judgment.
For with the internet, the collective Ego and Id of humanity were set free to share all kinds of things. Previous to the internet, most published work represented, shall we say, our collective Superego. It was a finished work, considered worthy of sharing, with the author/artist/producer adopting an auctorial mask which might be other than what he or she thought about to amuse oneself in the off-hours. Publication was expensive and complicated. It took a lot of capital to produce a physical book or a broadcast or a film. It took a ponderous distribution system to bring it to those who might pay to read or hear or see it. And if it were considered offensive, the collective Adults in the community might interfere with its publishing or restrict its availability to certain seedy sections of town. The Ego, which writes diaries and shopping lists, would lack sufficient customers who knew the author to pay for the costs of production and distribution. The Id, in which the dark trolls of our collective mind roll and frolic in all their polymorphous perversity, wasn't considered worthy of full production (though there was always a market for it, so it could never be entirely excluded from the mix).
Humanity's collective Superego is still well represented on the internet. News sites, opinion sites, blogs, and encyclopedia-like pages of information are all booming. But the internet also plumbs the Ego, with people publishing their diaries, their hobbies, even their shopping lists to share with their friends. "Meet you at Starbucks at 10:00" is now considered as worthy of universal publication as The Canterbury Tales. Oh, but the Id. The Id. The collective basement of our universal soul has been thrown open for all to explore on the internet.
Pornography of every description abounds. (As the song goes, "the internet is for porn.") But not just pornography. Hate speech and conspiracy theories and slander and altered photos/bios/fake news do, too. I'm surprised we haven't seen the rise of a dozen new, crankified religions since the internet took off in the 1990s. Maybe that would be too "meta," since the internet constantly invites the breaking of the fourth wall; it's very open to sly, sideways looks. But what religious stuff I do read often promotes the incredible. Too many heartwarming stories are just a little too pat to be believable. A disturbing thought creeps into my brain: is this how some of the formulaic saints' lives were written? What does the internet have to tell us about the invention of Tradition?
One thing is for sure: humanity only rarely un-invents a new form of communication, and then only for a time. What can be known, will be known, and what will be known, will be shared. So the real problem with what you find online isn't found in the pixels and bits of data we are consuming: it's found in Us. We only find out there what already existed within us, and the internet, like publishing, like art, like language itself, only reveals our Self to ourselves.
When you stare into the Abyss, the face that stares back at you is your own.