There are internet sources which are absolutely as good as print sources, because they are the same material - such as library collections or archives or the Encyclopedia Britannica. But internet speech is just speech. You wouldn't offer a random snippet of conversation overheard at a party as a source. Putting something in a blog, then having it reblogged by a blogger calling himself a "columnist" with a label identifying it at history makes speech look like more than it is.
However, if you read snopes.com on a regular basis, you know that this sort of copy-pasting occurs regularly in the print world as well. A large number of urban myths have seen print in a respectable newspaper which "heard it somewhere." Then whoever quotes that newspaper looks like they quoted from a reliable source.
Most people who are experts on something can read any mid-level book for casual readers on that subject and pick out half a dozen errors, because the writer of such a book is not usually an expert in anything but writing books for casual readers. Even professional historians suffer from entrenched errors which somehow get started in an academic community and become common knowledge without actually being true. Reenactment communities have their own kind of errors which "everybody knows" which aren't true. Very good and otherwise intelligent historians can make absurd errors due to being expert in a specific field, such as armor, and not knowing anything about a closely related field, such as clothing.
The internet has less fact checking than most publishing houses, but nothing is ever guaranteed true unless you check it yourself, and even then, it's only a statement that your source said this, not a statement that the source is valid.
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