Is there actually an Aesop, green or otherwise in Mothra? Looking at the speeches, there appears to be many. However, by the end of the movie all their Aesoping is rendered pointless. While characters claim the Earth is angry at humans for pollution and creates Battra to punish humans, the real reason Battra exists is to destroy an asteroid. Pollution is unrelated.
Even the story the Cosmos tell of the ancient civilization and their Weather Machine supplies motivations for Battra that the Cosmos and Mothra really do not know. It isn't until near the climax of this film where Mothra and Battra have a meeting of the minds. The Cosmos say the ancient Earth was angry and prideful, thus punished humans for daring to make a weather machine. However, there is no proof of that. What we do know is that the Weather Machine created a dangerous store up of energy and unspent storms. When Battra destroyed the machine, that unspent energy was unleashed. The unspent energy was growing over time. If Battra had done nothing, and 100 years later the Weather Machine experienced an outtage, the resulting storms would have been even more destructive. This is to say, though Battra's actions ended up slaying 99% of humans, Battra saved the human race.
We know for a fact that Mothra does not understand Battra until much later in the film. The Cosmos state that Battra is here in the present to penalize polluters, when by the end of the film that is clearly not the case. In fact, Godzilla VS Mothra: Battle for the Earth depends on multiple layers of misdirection regarding character motivations. The Green Aesop is itself another misdirection, setting up the tragedy of Battra's death.
The only evil directly related to pollution is Godzilla, who in this series is canonically created by radiation; either the splash of atomic weapons testing or the sinking of a Soviet submarine. Godzilla is the most satanic he has ever been in any film. However his violence is largely at random, and has no overarching intent of revenge or wraith.
We have seen in Godzilla VS Biollante and Godzilla VS King Ghodirah that humans are capable of checking Godzilla, though not defeating him. To the degree that there is an environmental message that is real in this movie, it is this: Godzilla has mortally wounded Earth's greatest defenders. If Battra is the sword of Earth, Mothra is the shield. And now both are gone, instead of just one. As it happens so often in real life, pollution is ultimately experienced for many as cancer. And that is what Godzilla is; he is cancer eating away at Earth's vitality and security. It is a subtle criticism of Pollution, but as it comes dressed in so many quasi-spiritual moralizings, it is easy to over look an authentically deep message. The shallow messages of environmental protection from so much of the cast are themselves misdirections to set up the awesome revelation of Battra's true intentions.
There is no sudden threshold of environmental destruction that will trigger a planetary smack down. Instead we are slowly undone as our security is compromised. The Earth seems actually indifferent to people and pollution. However, pollution creates Godzilla, and he is the means of our torment, not Battra. The Earth didn't create a monster, humanity did. But it is a monster that can be managed, through vast efforts and cooperation.
