So, a bunch of aliens come along and tell us this:
We are beings from another dimension. In case you're wondering, we are the ones who created the comos in which you live. We can destroy it instantly or let it continue on as is. Your choice."
We ask, "What, then, is the choice?"
"Just give us an 8 year old girl who we'll make immortal and we'll give you back your cosmos."
"What will you do with her? Whatever we want. Primarily, we enjoy torture. We'll torture her till the end of time. If you won't do that, we'll bring everything you know to an abrupt end. What is your choice?"
How would you analyze this? The greatest good for the greatest number or what?
"..have simply decided it would be a positive good thing to end existence now.."
I expect that many of the bloggers here have read 'The Hitchhiker's Guide to the Galaxy'. It clearly mentions a point of alien philosophy concerning the opinion that, 'it might have been a bad idea'.
For most species, this could clearly have been the case, for us, the jury is still out, but might be close to a decision. If the 'Fractal Nature of Existence' is true, our demise is simply a near by system state where we no longer exist. As we transition to greater and greater degrees of 'unfitness', this could slowly become 'true'. With the most delusional, the most 'superior', grasping at the last straws, as the curtain comes down, and their beach front property becomes excessively soggy.
If someone believes it would be a good idea to end their existence now, they are by all means free to do so. But they shouldn't presume to make the decision for everyone else on earth and the rest of the universe. And that's what's being discussed here.