I never feel guilty when I listen to music I enjoy.
I don't care that other people hate Britney Spears, Avril Lavigne, Green Day, Sum 41, Blink 182, No Doubt, Lindsay Lohan, U2, Outkast, Gretchen Wilson, Christmas Music, etc.
If I enjoy it, I listen to it. If you don't enjoy it, don't listen to it. If the critics/hipsters/indie/general-music-know-it-alls tell you not to like it and make you feel guilty, then stop reading what they have to say.
Be proud, stand tall and take a stance. Crank up Britney's greatest hits and dance around in your underwear - you will be a happier person if you do.