David Crosby is ensconced with a very elite group of musicians who used their songs and harmonies to end a war, discrimination and government wrongdoing. Bob Dylan and Joan Baez are others in this small group of troubadours that made a difference in the 1960's and 70's.
It's not enough that music is of a time -- it also has to be good on its own. The deep resonance of the chord changes, the perfect harmonies, master guitar riffs, intriguing lyrics... there are reasons these songs are still with us.
I love that Matt and Trey do not care who they offend in the pursuit of amusing themselves and a watching world. I support them with all my heart & soul right until the point where it puts me in any actual danger.