A fundamental challenge of the half-hour sitcom that's short on big story arcs is that the writers have to pretend everything is wrapped up neatly within the space of one episode. Sometimes that calls for serious hand-waving to pretend that something simply didn't happen.
It's supposed to be "sweet" that Barney's friends deceive him. They deceived him when the choir agreed to meet elsewhere, without telling Barney. Singling out one person and ditching them is the stuff of nasty school cliques, and not a nice thing to do to a friend. They deceived him by omission when they could have talked to him honestly (yet kindly) about his singing voice, but chose to let him make a fool of himself instead. They deceived him when they led him to think there was a special microphone he had to whisper into. They deceived him when they got someone else to dub his voice, while having him think he was hearing his own voice. They deceived the judges and audience at the competition too, by having them think Barney was the soloist - not terribly ethical.
One problem with that sort of lying is that everyone would have to maintain it over time - an element that was addressed in other episodes. They'd have to keep pretending he can really sing, and perpetuate further lies to stop him. They'd have to keep pretending that one microphone was different from the rest. Eventually, someone would slip up, and he'd realize that a bunch of people he trusted had been lying to him all along. Not exactly sweet.
But the writers took the easy way out, and pretended it'd never matter again. End of episode = end of consequences.
This would have been a much stronger episode if Barney's friends realized that by sneaking around and lying, they weren't doing Barney any real favors or acting like responsible adults.
It's supposed to be "sweet" that Barney's friends deceive him. They deceived him when the choir agreed to meet elsewhere, without telling Barney. Singling out one person and ditching them is the stuff of nasty school cliques, and not a nice thing to do to a friend. They deceived him by omission when they could have talked to him honestly (yet kindly) about his singing voice, but chose to let him make a fool of himself instead. They deceived him when they led him to think there was a special microphone he had to whisper into. They deceived him when they got someone else to dub his voice, while having him think he was hearing his own voice. They deceived the judges and audience at the competition too, by having them think Barney was the soloist - not terribly ethical.
One problem with that sort of lying is that everyone would have to maintain it over time - an element that was addressed in other episodes. They'd have to keep pretending he can really sing, and perpetuate further lies to stop him. They'd have to keep pretending that one microphone was different from the rest. Eventually, someone would slip up, and he'd realize that a bunch of people he trusted had been lying to him all along. Not exactly sweet.
But the writers took the easy way out, and pretended it'd never matter again. End of episode = end of consequences.
This would have been a much stronger episode if Barney's friends realized that by sneaking around and lying, they weren't doing Barney any real favors or acting like responsible adults.