"Lots of hippies seem to want to lower everyone's standard of living for the benefit of the planet. Plus many of them seem to be unable to grasp the notions of conservation of energy, the second law of thermodynamics, and efficiency. Those are the reasons that I normally see for anger towards the envirofolks."
Maybe the hippies understand the numbers game. Since 1970, the population of the world has essentially doubled. Now given that there hasn't been an equivalent growth in resources then that means there is less available for each individual. So if your lifestyle exceeds your share of the resources then you need to cut back in some way.
I keep hearing this wonderful fear-mongering phrase "lowering your standard of living" but it is hardly ever pointed out that our standard of living (in the developed world) is ridiculously high already, how many cars or computers does one family need? 'Er indoors and myself have 3 computers, a car, a motorbike, 2 push bikes, 4 MP3 players and 2 hi-fi systems (just a quick tot up of luxuries). Now if we got rid of some of these then our standard of living would drop but we could probably live quite easily if we halved that list. Try auditing your own stuff and do the old spec design exercise of determining what is required and what is just desired.
"Lowering your standard of living" != "living in a cave".