I don’t know why he thinks that, but he is probably correct that in their own minds they believe that their cause is just and they believe that they are doing good.
But only an unthinking fool believes that man is capable of destroying the planet. Even if every nuclear weapon ever built were detonated on the same day man would not destroy the planet.
It could be a Mass Extinction Event but the planet would endure and life would again spread across the world. Should they end oil there would be world wide famine and the industrialized world would come to an end. A Mad Mask type dystopia would result. People would kill each other for scraps.
What we need to know of these people is what is the Good that they are trying to accomplish. Are they trying to save Mankind or are they trying to save the present ecological make up of the world?
If they are trying to save mankind, I agree with the author that they are going about it in a way doomed to failure.
If they are intending to save the ecology of the world they are also doomed to failure because the ecology of the world is always changing and mankind is impacting the ecology less today than it did 30 years ago while supporting 4 billion more people.
These young people have been poorly educated and are to be pitied and ignored; maybe imprisoned for misdeeds. But certainly not listened to.
“…but he is probably correct that in their own minds they believe that their cause is just and they believe that they are doing good….”
That’s the problem, they are entirely in ernest and will stop ant nothing to bring about their promised land. They’re fecking crazy, in short.