Answers to my questions（4）

 10.  Did singers united to against music censorship/? If so, does it have any effect?
In the end of 1980s, many heavy metal singers got together to against music censorship and PMRC , Dee Snider,  John Denver and Frank Zappa were the main advocates. At last they come to a decision that instead of strict censorship the PMRC were allowed to put a label on albums said"“Parental Advisory explicit conten"

here is a movie on youtube about how singers fight against the PMRC
Warning: Parental Advisory . 2002. Film. 25 Jul 2012. <http://www.youtube.com/watch?v=b3qdtC91ss4&feature=relmfu>.