Of course, Rush doesn’t set a tape going and then play along with it. The different sampled elements are all separate from each other, and each is triggered individually via foot switches. So it’s on them, right at the proper moments, to step on the right switches at precisely the right times during a song.
They Might Be Giants was famous for having two guys and a tape player as their entire lineup for over a decade. All percussion, synthesizers, and the various wacky samples they were fond of utilizing were reproduced live by hitting play on the tape; the band themselves just supplied vocals, rhythm guitar, and accordion. In fact, they were criticized once they acquired a real backing band (something I don’t really think was deserved, as they did produce at least two fantastic records after abandoning the tapes and MIDI keyboards).
That’s also what U2 does, to trigger extra guitars or string loops. This has caused a fair amount of controversy amongst the fan community, particularly the between “U2 must remain pure and untainted” and “U2 can do no wrong” camps. I fall pretty much in the middle ground - I don’t have any problems with bands using taped elements within reason, but on the other hand I don’t go to concerts to hear the album version with some added crowd noise, I go to see a band play live.
I think I draw the line at artifical guitar overdubs. Like you say, it sort of defeats the purpose of seeing a band play live if they’re not actually, y’know, playing the parts you hear. Sampling and using a backing tape (a la They Might Be Giants) to achieve sounds that you can’t possibly generate on-stage with your given set of instruments is fine by me, though.
If you think about it, if you’re using a synthesizer, you’re already “faking it” to some extent. I’m sure there was squawking the first time a band used a synth to reproduce a string section or even an organ.
Samples are a great tool for a live band. I’ve seen wonderful shows that were almost nothing but.
Not really. People had gotten used to mellotrons, so a synth was pretty much the same thing (and a mellotron used tapes).
Back in the old days, a live show was expected to sound different from the record; that’s why you went. Groups that slavishly followed their recorded sound were derided. So using a substitute for a studio sound was not objected to.
Now, people want to hear the exact same thing as the CD. No wonder people use tapes.
I think there’s more to it than just an attempt to perfectly reproduce the recorded version, at least for less well-off artists. I keep bringing up TMBG, because they’re as apt an example as any I can think of, but their reasons for using tapes had as much to do with the expense of hiring live musicians (not an insignificant amount, when you’re a pair of dirt-poor kids from Brooklyn who write songs in MIDI) as any artistic impulse. They had the option of doing either all-acoustic shows or using a tape, and chose the latter because the nature of their music requires the energy you get from oversized stacks and blasting percussion.
Going on memories from more than 25 years ago, you’re right that ELO were criticized for doing this but (if I recall correctly) one of the problems was that they never acknowledged that they were using backing tapes, even when they were called on it.
As for the OP:
Using backing tapes when you admit it (or at least not trying to hide it): OK.
Using tapes to recreate that killer guitar solo when your lead isn’t even plugged in: Not OK.
I’ve performed EBM (think techno with words) and industrial musci live. NO way in hell this can be done without most of it already set to go.
Let’s say you record a song. It is likely to have anything from 10-60 tracks. Live? Most of those tracks are coming with you, pre-recorded
I got the question right! I don’t what all that music talk is about. 
I got the question right! I don’t know what all that music talk is about.
When you see the band VNV Nation live (excepting the last tour when they had two live keyboardists), there is a vocalist and an electronic drummer. That’s it. The rest of the music is on a dvd with backing movies. It sounds strange, but they’re one of the most fantastic live shows I’ve ever been to.