"The old marxist leftists at least believed in technology's possibility in advancing the status of mankind. They spilled rivers of blood and oceans of ink defending the idea that all the people on the earth could have shoes from one modern shoe factory...and all that stood in the way was the capitalistic concept of private ownership of the means of production."
"But, when the leftists discovered the undeniable truth about their system's productive capacity vs capitalism's...they turned away from industrialization, and declared that it was better for man to go barefoot."
Basically, in a nutshell, that is the underlying origin of leftist environmentalism: sour grapes. Their utopia was revealed to be a fraud, and now they have turned away from progress altogether.