See YouTube Through History
If the internet had existed in caveman times, we would build a time machine (because if the internet existed that long ago, clearly we would have time travel technology by now) and travel back and un-invent it. Sure, we would probably blink out of existence (can't think about it too much -- time continuum stuff gives us a headache), but at least none of these horrible videos would have been made.
As this video from Above Average Network shows, YouTube would've been pretty much the same had it been around before the invention of modern plumbing. Cleopatra would be clogging it up with her cat vlogs. Historical figure like Christopher Columbus would take the "Cinnamon Challenge." Footage of the Hindenburg disaster would be dubbed an "epic fail" by commenters. Basically business as usual. Time-sucking, bizarre business as usual.