The sum of all knowledge and the sorry state of the web
IMO the worst side effect of current web of knowledge is what I'd call the illusion of knowledge. When it was more difficult to access and publish information, that imposed a much higher bar on what was being consumed. These days, people watch a 10-minute YouTube video or read a reddit comment or twitter thread and believe (perhaps unconsciously) that makes them knowledgeable in said topic. They will then, in an absolutely confident tone, display their expertise by answering questions and stating their opinion as if it was 
a fact. More people read this, and the cycle begins.<p>You see it all the time on HN and other forums. If you're an actual expert in a specific (usually scientific) subfield and you read comments about an article in that field, you find that a large percentage are not just factually wrong, but also written in an extremely confident tone by people who have probably studied the topic for about 10 minutes.<p>By having easy access to all this information people have stopped being humble about what they don't know.