Although it may not be how they perceive themselves, I like to see druids as proto-wizards, practitioners of an old magic predating the division of arcane and divine magic.
Their magic exist independently from the god-channeling powers of clerics but is much more "raw" than the isolated and refined magical essentia (insert magico-babble) that arcane wizards use. The essence of druidic magic is still strongly tainted by the physical world through which it transits, thus limiting druids to spells with strong natural overtones. Modern druids are the moral successors of those who saw this lack of "magical refining" as a boon - or like we like to say - a feature, not a flaw. Objectively, this "natural taint" allows for spells that arcane wizards cannot cast.
As such, I see druids as spellcasters that need nature more than they worship it (although this need led many druidic cultures to worship or revere nature as well). Destroying nature = cutting off their power source so of course they will protect it, but not all do it for the love of trees and squirrels. As a matter of fact, I had druid villains that considered wilderness as a necessary nuisance.