If I were a budding singer and had the chance of Simon Cowell's opinion free of charge, I would jump at it, and listen to what he said.
He is honest - and he is looking for talent because talent makes him money. If people are deluded by their friends and family into believing they possess talent and they don't, then an honest opinion from SC should put them out of their mistery. No amount of wanting your loved one to be good when they are not outweighs an objective opinion from a man who clearly knows what he's talking about.