Dear Luis,
I didn't hear about this, but if this happened, try to consider other point of view too.
See: It's absolutely not about band being disrespectful to their fans. It's about principles. It takes years to learn to play instruments, you have to care about it, buying new stuff for it, spend a lot of time and money. Then you got family, house, bills. And if you are lucky you can make some living from it, to pay the bills, to buy another equipment to work (yeah, although audience is having fun during the gigs, so does the band, it's also a job, you know). And everyone should be paid for doing a good job.
Imagine they would go on the stage that day knowing they don't have a chance to be paid - then this would become more common - word does spread quickly.
I also work for some bands and I can tell you that if this would happen to any of them, I wouldn't let them on the stage too.
It was disrespectul from the promoter and going on the stage after that would be like supporting this behavior.