The idea of celebrity is neither all good nor all bad. It's mostly bad that we idolise actual people to a superhuman level and then follow them around in a self-selective big brother. They can do no wrong, until they do, and then we either hypocritically turn a blind eye or ostracise them for making a human mistake. It's okay to publicly humiliate people we've never met on a mass scale because they're famous. "Normal" people just don't have this problem.
On the other hand, celebrities who contribute their art and insight to culture are often vital to a person's life. Especially a young person. In formative years the people we see, the music we listen to, the films we watch, the books we read all make up the personalities that are growing within us. We attach ourselves to celebrities because they attract us with qualities we like about us, or that we aspire to have about us. Young people who are totally unsure as to who they are need celebrities to make them feel even an ounce of normal. They need role models, essentially.
I felt devastated about the news of David Bowie's death because I'd let him become a big part of my life. He'd been there in my parents' life for a long time so his music made its way into mine eventually. I don't have anything profound to say about him other than that his fashion, his music, his attitude so completely embraced art that I can't think of any other way to live well. He was there right in the middle of the colours and the instruments and the sounds and the waves of culture, taking it all in and throwing it all back out at us right up until the end. People threw street parties on the day of his death to celebrate that vibrancy of life and art. David Bowie was a "good" celebrity because he did it all his own way, and we all basked in his artistic glory. We didn't all follow his private life like dirty stalkers, but we took what he gave us and that was enough.
People need inspirations like David Bowie to enhance their own experience of life and art. We don't need their body shape, or their last boyfriend, or the dress they wore to that awards show, but if they're handing out the brilliance of the inside of their mind for us all to share then they are important. We all need brilliance.