It's also worth noting that misinformation can spread very quickly. It takes no effort to click "reblog" and then forget about a post forever. On other platforms with this weakness (such as Reddit), there is incentive to discredit incorrect information (you get a lot of comment karma if you do this on Reddit), but there is little incentive to do so on tumblr. Any commentary on a post is not inherently tied to future reblogs of the post, and users can edit the content of reblogs to make it look like that content was written by the post's original author.