This really annoys me. Ive heard people say bands they don't like are rubbish and 90% of thevtime, they just mean "this band doesn't fit my taste". If they've made it to the radio/tv/big festival then its highly unlikely they are rubbish.
Personally I don't like Taylor Swift but I appreciate she is excellent at what she does. I really can't stand classic rock but those bands probably influenced the bands who influenced my favourite bands.
Simply Red however, are just rubbish.