This is a rather overblown parody of male yuri fans, A big in-joke for fans about fans. As such, it can sometimes be more biting than funny. Like, MC shares all the possible traits of male yuri fans, including those used by (not only) female yuri fans as exclusion fuel. It's rarely found in anonymous communities, but sometimes crops up in pseudonymous ones. Female yuri fans (like Mrs. Friedman) exhibiting derogatory attitude about male yuri fans, going as far as calling them "creeps", "losers" and other names, all in effort to insinuate that male fans are not TRUE fans, and not TRUE target audience for TRUE yuri.
Additionally, ire towards this manga may come from it repeating the same joke for too long AND moving in a direction some feel inappropriate for something running in a yuri magazine. I.e. having all yuri developments in it be entirely MC's fantasies, or having girls happily hook up with guys in later chapters. Admittedly, I have no idea what happens in this manga as I didn't read the raws, but judging by first two chapters (i.e premise and it's execution) and the fact about 5 volumes being out, it might heavily be the former.
All in all, combination of biting satire/parody, same joke for too long, and lack of actual yuri developments in a "yuri" manga might be what contributed to such heated reactions from some of /u/'s denizens.
P.S. Five volumes, man, FIVE! That's 3 more than Strawberry Shake Sweet. 3 more than Hanjuku Joushi. 4 volumes more than Ebisu&Hotei.