Environmentalism seems qualitatively different from everything else here. Is there some baggage to this beyond, say, conservation, or assigning plants and animals some moral weight, that is intended here?

Not really, aside from the standard observation that you can just as easily play the 'find cult markers' game with environmental groups like Greenpeace or ELF. Cleansing rituals like recycling, intense devotion to charismatic leaders, studies of founding texts like Silent Spring, self-abnegating life choices, donating funds to the movement, sacralization of unusual objects like owls or bugs, food taboos ('GMOs'), and so on and so forth.