I'm certainly late to the party, but I completely get what your were getting at Paj(much clearer than mud to me). I absolutely love The Violent Femmes, but getting right down to it, the music isn't good. It's abrasive erratic and at times poorly written, but it all comes together in the most enjoyable way.
A different example without using Hitler would be the Earth Defense Force games, bad games when compared to common standards, and if Halo or CoD did some things like EDF they'd be slated for it. EDF however, is just bad enough to be hilariously fun. Thousands (since I doubt it sold millions) of people love it, mainly because it's bad.
B-Movies also fall into this trope. Although, I do think music gets a bit of a free pass on this. I don't encounter music of that type as often as I do other mediums, so I'd guess that most people buying Bieber quantify his music as their definition of good. So in a sense with music, popularity="good".
Eventually his voice will drop though and his music will no longer be "good". :p