Anyone who knows anything about Harry Potter fandom in those years knows that its readers were always thirsty for something new in the Potterverse to read or be exposed to. By latching onto that universe's incredible popularity, Yudkowsky exposed a large number of young, inquisitive people to the ideas of rationalism. It was essentially a recruitment mechanism, one that was wildly successful. Many rationalists freely admit that their first exposure to rationalism was via HPMOR.
Anyone who knows anything about Harry Potter fandom in those years knows that its readers were always thirsty for something new in the Potterverse to read or be exposed to. By latching onto that universe's incredible popularity, Yudkowsky exposed a large number of young, inquisitive people to the ideas of rationalism. It was essentially a recruitment mechanism, one that was wildly successful. Many rationalists freely admit that their first exposure to rationalism was via HPMOR.