"The point is," writes the Tumblr user, "the Dursleys were just minding their own business when a horcrux was dumped on their doorstep. For the next decade it proceeded to warp their minds, turning them from your garden variety insufferable human beings into horrible, heartless monsters."
Personally, we're not convinced. While the horcrux thing does seem to be somewhat of a plot hole, why weren't the Weasley's completely awful to Harry when he was in their care? Not to mention every person he interacted with at Hogwarts, who -- with respect to the fact that the great good vs. evil battle he was involve in descended the institution into total chaos -- was relatively cool to him.
(To be fair, Snape had his own things going on, which, if you have 14 minutes to sob uncontrollably you can watch in chronological order here.)
The fan who posted the theory even admits it is all satire, writing, "Allow me to state for the record that the above description was intended to be read as satire. I do not honestly believe Harry is responsible for the abuse he suffered, nor do I seriously consider the Dursleys to be noble and virtuous heroes."