Why doesn't Justin Bieber smile in most of his pictures now?
Too much fame too early in life can only be described as dangerous, at best. How can it be healthy for a person who is in the process of growing up to be confronted with fame and its intense pressure that would weigh heavily even on a seasoned adult? It is not natural, and it is happening to too many young people.
I'm sure it was dazzlingly wonderful for him at the very beginning. Now, he has no way of knowing what people around him really care for him and about him, and which ones are interested only in sucking up some of his fame and influence, or who are desperate to get in on the 'cash cow' that is his current career. It is asking too much of a young person; many adults have been driven to ruin by the same pressures.
He can't rely on his managers or agents for advice: they are watching the $$ fly in, hand over fist.
Don't hate him for being human; in some small way you have contributed to victimizing him. When masses of people turn others into gods, demonizing is not far behind. He is probably in a daze now, constantly, and not even as a result of drugs. Rather than hating him, how about hoping and praying that he survives to adulthood? Maybe there is still a good career ahead of him after he matures and seasons.