Discovery doesn't use fossil fules. The main engines are powered by oxygen and hydrogen and the solid rocket boosters are made up of ammonium perchlorate, aluminum and iron oxide.
I can also guarantee you that fossil fuels were used in the production and distribution of the rocket boosters and that the airplane the video was taken from wouldn't be flying if it didn't have any jet fuel in it's tank.
Humans are smart creatures, but we shouldn't kid ourselves into thinking we would be where we are at now if it weren't for a cheap, albeit limited, supply of highly concentrated energy.
That we are wasting energy which has been stored and untapped for hundreds of thousands of years? Do we really expect that our ancestors will be better able to exploit this value than we are... without our given expliotation? Will this be true forever? Should we just let that stored energy remain forever?
Ceteris parabis, we will extract exactly as much value from our ancestors as makes sense. And our ancestors will do exactly the same. I do not begrudge them that any mire than I begrudge us this current state of affairs.