Rock and roll has been the music of rebellion and social change since the 1950s, and each successive wave of youths have discovered its power (chords) and embraced its do-it-yourself aesthetic. Punk rock and technology, from cassette tapes to MP3 and file sharing have made music the most easily understood and easy to identify mode of rebellious self-expression. The music, lyrics, and yes, fashion have been and are still threatening to the powers that be: Los Angeles Police chief Daryl Gates viewed punk rock, especially the band Black Flag, as a major threat, regularly sending in riot cops for their shows and says Black Flag drummer Greg Cameron: