Some of them are, which is why it's important to look at the sources and verify for themselves. Citing a news article provides a very different level of evidence for an assertion than a peer reviewed paper.
Of course they are. Which is why every scholar should cite where they found their information, so that readers can chase down the reference and critically examine it. Authors should cite the source whether it is a blog post, a newspaper article, a popular textbook, a journal paper, a historical accounting document, or private correspondence with a colleague.
When people don’t cite their actual sources it becomes orders of magnitude more difficult to figure out how they came up with their claims and trace the origin and transmission of those claims through the literature.