Because the people on tumblr seem to be the most gullible single group of people on the planet, we need to single them out when it comes to mocking people who believe everything they read. Be it SOPA, bad photoshops that convince people that ads in the 1940s were unintentionally filthy, or that "HUVR" boards are coming out this Christmas, tumblr users are all-too-eager to believe anything that comes across their dashboard.
I'm a tumblr user myself, but it makes me sad to see what a bunch of idiots the site is full of. After all, this is how Republicans win elections: they make ridiculous claims and people blindly believe them because they're too lazy to fact check anything.