The same kinds of people who admonish you for taking an elevator because it's bad for the environment, even when your legs are sore from cycling to work.
This is true about almost all human groups/movements though, and I'm not sure that environmentalists are more guilty than average.
But people who drive to work everyday still try and lecture me over nothings like putting a laptop on standby overnight.
I live within 8 miles of the office and subsequently put about 4,000 miles on my vehicle annually. I consume less fuel than 90% of the people in the office with new 'environmentally friendly' cars who live 40 miles away, yet it is I who receives the rash of shit. /rant