Admiration is, like most things in life, useful in moderation and deadly in excess.
When directed towards proper figures, towards beacons of human ability, understanding, and kindness, such as Gandhi, Mandela, or MLK Jr. That admiration can inspire others towards self improvement, determination, and kindness towards others.
When that admiration is directed to dangerous places, such as a young child admiring a particularly charismatic criminal, then it becomes dangerous. It encourages people to act in ways detrimental to themselves and society.
What should be avoided, I propose, is admiration based purely on emotion and whim. You shouldn't look at a person and admire them simply through charisma and good looks, you should observe their character, their actions, what affect they have on others, and by considering how you feel about those things you should form your admiration.