I'm sure it's no different on any other platform, so I hope this comment isn't seen as some way to skewer tumblr for being unique in this regard: but the number of times I've stumbled across content spreading some nugget of content about a health-condition, mental state of being or current event that is OBJECTIVELY untrue getting eager reshares and comments applauding the original poster that would cause any trained professional to expire from the horror is staggering to behold sometimes.
Again, not unique to tumblr, not here to suggest it is, but since it's the focus of the conversation we're having, there it is.
Already I've seen people I follow talking about leaving the platform because of this decision, which is going to hurt my own blog as I rely on them to discover new and interesting content (not porn, but I'm a big fan of futurist artwork, giant robots, Ralph McQuarie style space paintings, stuff like that).
My observation is that what I can only call information operations on Tumblr are very similar in form to various groups retweeting divisive political memes on Twitter or other social media. Most likely it has been freelance individuals with some sort of sexual fetish, not an organization, but still. It's not normal user behavior to be constantly re-posting and mashing up memes all day long every day encouraging pre-teen girls to be anorexic.