Having used online media for well over three decades, much the opposite.
The "don't trust what you read online" meme is a persistent one, but it's also long been reactionary and incomplete.
1. Yes, there's disinformation on the Internet. Shocking, but true. And yes, the ease, scale, scope, and speed of online disinformation dwarfs all previous media. And while I frequently argue that scale matters, we can at least point to the fact that the mechanism isn't a new one: rumour and disinformation networks predate mobile, the Web, Internet, electronic, and print communications technologies.
2. From early days, the Internet was very often where both disinformation and rebuttals were most available. Two specific incidents I can recall by memory: the Pons-Fleischmann "cold fusion" paper, in 1989, and Intel's Pentium F00F bug (Spectre/Meltdown aren't their first on-die rodeo) (1997).
Each was distributed widely online, though largely via non-Web protocols. I received a copy of the Pons-Fleishmann paper two days after its release (stunningly quick for the time) via FTP. The F00F bug was circulated on mailing lists, particularly those concerning any kind of numeric programming, several days ahead of general news release.
3. "Online" is simply a channel, and use of the term conceals more than it reveals. Harold Lasswell's five-questions approach to content analysis is useful: "Who says what, to whom, why, to what extent and with what effect?"
That is, in online comms, known and reputable sources, speaking on known and reputable channels, tend to be more trustworthy than unknown and unreputable sources speaking on unknown and unreputable channels. The risks of impersonation and mimickry are real and actual, yes, but also the general notion that if someone is claimed to have said something but denies it, you might want to check assumptions. Similarly, the message itself ("says what"), audience ("to whom"), and actual or apparent intended outcome ("with what effect") are also relevant.
(See generally: https://en.wikipedia.org/wiki/Content_analysis)
The simple fact that a thing is said online doesn't of itself make it more or less credible. The elements of content analysis are a far more useful guide.
Verification of information acquired online is often also going to involve online sources. Though offline may also come into use.[1]
4. Reality is that the Internet (increasingly apps) and Web are now where most communications happen. Both legitimate and valid, and illegitimate and invalid, messages are propagated. As my friend Woozle put it a few years ago:
[B]ecause of a high percentage of the population being present, there is now substantial power to be had by influencing the discussions that take place.
That's now true of the Internet, though it's true of any medium. Cable TV, talk radio, Citizens Band, television, radio, magazines, books, pamphlets, church sermons, theses nailed to parrish doors, and the like, have been used through the ages. Art and music likewise: Michelangelo operated a propagandistic arts factory for the Medici, and liturgical music and classical art were an arm of Church propaganda (in both the original and contemporary meanings of the word).
The three most published books in history are all propaganda, again, in original and contemporary meaning: the Bible, the Koran, and Chairman Mao's "Little Red Book" (The Sayings of Chairman Mao), each with billions of copies printed.
Facebook more messages to more people than that, every few days. It is the largest propaganda engine ever created.
Oh: and some of the earliest online abuse was organised around political and cultural conflict and genocide.
See Dorothy Demming, "Activism, Hacktivism, and Cyberterrorism: The Internet as a Tool for Influencing Foreign Policy", ~1998:
http://www.iwar.org.uk/cyberterror/resources/denning.htm
Documented as well by Howard Rhiengold in 1993:
http://dlc.dlib.indiana.edu/dlc/bitstream/handle/10535/18/Th...
An account is also included in John Quarterman's proto-history of the Net, The Matrix (1990):
The most striking use of the Matrix [Quarterman's term for online communications networks, Ed.] occurred to late to be described elswhere in this book. When the Chinese govenrment cleared Tianamen Square on the morning of 4 June 1989, reports of eyewitnesses were sent out by Chinese students by telephone and facismile within hours of the actual events, typed in by Chinese students abroad, and immediately broadcast throughout the world on dozens of networks and maling lists....
Though cautions of excessive credulity over online communications are valid, I strongly suspect that at least some of the impetus for that particular caution comes from powers and institutions which are challenged by a communications channel they can not directly control. This can, at least at times, have benefits, though the rise of the Net itself as a locus of surveillance, control, and manipulation is to my mind among the biggest stories of the past decade.
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1. For an example of a meme debunking, there's a case of a now 127-year-old hoax which still has legs. Some 18 years after its initial appearance, the hoax was being re-publicised by a US congressman, and I believe entered into the Congressional Record -- just to show that even well-known and highly-institutionalised sources can get things Very Very wrong. All this for a bit of political fluff tossed out to encourage attendence at a party meeting. The "Banker's Manifesto of 1892" hoax:
https://old.reddit.com/r/dredmorbius/comments/39w8u4/jp_morg...