In my opinion, the only disadvantages of fashion when it comes to young people is that clothes can sometimes act as a negative divide between people.
Especially in a school setting, clothes can be seen as a "status symbol" - where the more expensive or popular clothing trends are seem as acceptable, whereas clothing that doesn't fit that profile can prove unpopular.
Another issue that is common in schools is the "appropriateness" of certain fashion trends. When most music videos and these days contain scantily clad women dancing in their underwear, it can be easy for impressionable young women to think that dressing this way is appropriate for everyday life.
Fashion and violence
Certain colors and outfits are associated with gangs and violent groups.
Young people may inadvertently get sucked into that world through an admiration for the style and fashion that these lethal subcultures portray.
Fashion and young workers
Finally, young people in third world countries are negatively affected by fashion through the "sweatshops" and inhumane conditions that the fashion industry imposes on young workers in order to trade more profitably and make even more money for themselves.