What is the disadvantages of mass media to the youth?

Well I believe it comes down to the parents or guardians to began with. Of course younger generations shouldn't be watching as much TV if at all.

Most of the primetime shows and stations are becoming more and more passive on what not to show. Having younger children subjected to nudity, cursing, sexual immorality, drinking and other negative adult oriented material is of course unsuitable, heck even unsuitable for adults at times. If the parents let their children watch inappropriate shows on TV I'm sure studies have shown the likelihood of these children being involved in such problems later on in life. (sorry can't quote any)

"Also the significance of poor grades and schoolwork
Because television takes time away from reading and schoolwork it's important to control TV viewing during the school week. Studies show that even one to two hours of daily television viewing by school-aged children has a significant harmful effect on academic performance, especially reading." - Canadian Paediatric Society, 1999

That was also almost a decade ago. TV has developed into a far more negative presence since then.
fixed answer so unreliable
hope my scattered brain explainations answer something

From,

Muhammad Nadeem Anwar

Asad colony, Sheikhupura Road, gujranwala, Pakistan

pacificschools@Yahoo.com