Your example of “Destroying the planet” interests me, because in Christian theology (not mythology) there are several senses in which human sin already has destroyed the planet.
As you know, I don’t believe in “Fallen nature” - God’s natural Creation remains “very good”, according to the Bible. But for that very reason we ought to be motivated neither to damage it physically, nor to over-exploit its resources, nor to pervert it morally. In that theology mankind is the custodian of earth, placed here to bring it to perfection in Christ. No need for further motives to cherish it, surely?
On that theology, human corruption reaps a reward of environmental problems (at least in part) as a matter of judgement, not simply material cause and effect, the most direct fault being our determination to bend nature to our selfish use rather than cultivate wisdom in its use.
If, though, one believes nature is fundamentally flawed (either by the Fall or by “selfish” “indifferent” or even “hostile” nature) then (a) you won’t love it and care for it as you should and (b) you’re tempted to the hubristic idea that humans can improve on it by main force.
The problem with the “save the environment” myth is that it is essentially Promethean - “Only our own efforts can get us out of this mess.” There’s no place there for repentance or trust in the governor of Creation.
The myth also has a tendency to redirect responsibility for the problem itself: why is the world a mess? Too many people (because the unscientific Catholics won’t advise contraception), too much ignorance (because the proles won’t use GM crops or the latest technology) etc.
But the truth is that the main cause of greenhouse gases is the long-term effects of 19th century science and its dependent technology (both of which fuelled the myth of endless progress), and the rise in population is largely due to early 20th century science (the Haber-Bosch process, originated for high explosive production and now universal for artificial fertilizers, using more fossil fuel in a vicious circle).
So pitching the story in the old Draper-White manner - “only the knowledge of science can save the world from traditional ignorance” - is simply throwing another fix of the same thing at the problem. We do, of course, need scientific input, but the myth hides the facts of science’s inherent limitations and faults, making misdiagnosis far more likely and the solution more easily missed.
And, as I said, if the problem is at heart spiritual, then the false premises of the myth sends us entirely in the wrong direction. Therefore, the stories by which we live must be founded on truth.
Where I disagree with JohnZ is in the definition of “Myth” - I believe we all live by stories, and the stories we live by are, culturally speaking, our myths. And they can be true, false, or something in between. All stories, necessarily, are selective in order to stress what is significant.
In the case of the Great Escape, for example, it was a real event, with some real “mythic” significance for British morale. A historian will be interested in (for example) some revisionist sub-plot about people being cheated out of their chance to take part, or bottling out at the last minute. But it’s not biased to tell the story in the simple, mass-heroism sense of the “legend”, because it’s essentially true.
Of course, had the Nazis won the war, the story could have been told as an example of British perfidy and terrorism…