OK, Mr. Punisher, pretty well spoken. I have to agree with your analysis, though I have to disagree on several points.
The 50s - not a bad start but rampant commercialism actually played a big part in destroying the early beginnings of rock and roll. Knockoff vocal groups, often singing songs written by a very small group of writers and played by a very small group of musicians, led to a lukewarm blend halfway between the roots of rocakbilly/soul and the full-on commercial pop product.
The 60s were the next variety of rebelling against the previous rebels. You are correct in saying that pot/LSD played a part in ruining the music, but the directly dampened creativity was to me a side effect. Rather, artisits such as the Beatles came to realize that they could record any old crap that came into their heads, and still be popular. Thus, developing artists spent their time trying to duplicate the crap spewed from above rather than creating.
I agree with your point about funk, which has remained some of the highest-energy music ever created, and requiring incredible musicianship to write and play. Disco, however, was for people too coked out to car about anything but a bass beat, and has translated directly to the awful trance/techno/rave stuff of today. Music made to stretch your buzz just a little farther by vibrating your brain into numbness.
However, 70s rock really just can't be forgiven, with a few notable exceptions. Mostly it is pretentious, over-technical, over-slick album fodder. Mostly it served only as something for punk bands to hate, and to point them back towards a simpler, rougher form of musical energy. This process was repeated almost exactly 10 years later as Grunge grew out of the (once again) glossy slickness of the 80s.
No argument here about your analysis of the late 90s/early 00s. Spot on.
Throughout the whole time, it is a continuous process of interesting ideas being offered up and consequently exploited. Not that this is news to anybody.