There shouldn't be a distinction between "pop" music and "popular" music, just as there is no distinction between "bad classical" music and "good classical" music - it's all just classical.
Pop music/popular music is any music that is written with the intent of being listened to by a wide audience for purposes of entertainment. In this way, some contemporary classical music is popular music (see Jennifer Higdon's Concerto for Orchestra). What I think separates the good from the bad is the amount of real thought that goes into the composition/arrangement/performance of said music. Take for instance, the following YouTube clips:
2 Foot Yard, by Carla Kihlstedt, a classically trained violinist, and member of several pop music groups including the Tin Hat Trio and Bay Area art-prog-rock-metal group
Sleepytime Gorilla Museum.
This music is not the kind of thing that can just be thrown together. The rhythmic and structural complexities exist, as do the melodic and harmonic ones. And yet it's designed to be heard by a wide variety of people, for entertainment. And it is entertaining, whether it's soothing on the ears, or grating.
I feel it's simply up to the audience to discern the good from the bad, according to their tastes. At the same time, it's up to the audience's friends to guide their tastes, because if someone grows up listening to Britney Spears, they're not necessarily going to like The Mars Volta - so folks, broaden your friends' horizons!