Compared to Elephant Cavalry, helicopters are much worse. The problem with elephants, though, is that they can't fly, and thus cannot cross steep canyons or swift rivers, or snowy mountains. The question of environmental friendliness is moot unless you can propose alternative means of accomplishing jobs that helicopters usually do. If your boat was sinking 100 miles out to sea, would you ask the Coast Guard to send a rowboat to get you and keep that helicopter on the pad because you are worried about its engine contributing to global warming?
Just ask Al Gore why he flies a chartered private jet instead of a commercial airliner when he goes to deliver a speech on global warming.