Very well put. I don't mind a band having a backing track like a keyboard, synth or something. But I want to hear the band play live because it's important to me that the music is being created RIGHT NOW. That's why we see live music. The music, the energy, the band, the crowd, it all feeds together into something bigger than the notes and the amps and the screams. It's important that it's live, and the worst that I've seen is when the entire band is live, but the singer is dubbed. I've seen this with some otherwise good bands (Within Temptation), and I just don't understand. Make the music on the stage, I didn't pay to see a band pantomime.
At the same time, I recently played a show with a band that had all of their guitar gear in a big rack (2 AFXs, in-ear monitors, and a Surface tablet). The band was a traditional 5 piece, except there were 4 guys. So they were missing a bass player. One of their guitarists laid down the bass on their album, and the band played along to a recording of the bass all night, with a click going to the drummer's earpiece. This is probably borderline for my tastes, I'd do it in a pinch, but ultimately I'm going to want a bassist up there live with me when I'm playing.