A Little Brainstorming For The Girls This Time...

[Jorlem]

Shepherd wrote:

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Jorlem wrote:

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Spoiler [+]
IIRC, Kyubey says or implies something to the effect that humans are the first species they found, when they went searching for an energy source that violated thermodynamics, when he is explaining everything to Madoka.  He also says something along the lines of that when humanity joins the greater community among the stars, there will still be stars for them to do so thanks to the sacrifices of the magical girls.  So it isn't just them, and destroying humanity wasn't the original plan, but the opportunity  to get everything they needed at once was given to them on a silver platter.  Remember, Madoka's super-witch couldn't have existed without Homura distorting karma.  Also, the series finale literally involved the total destruction and rebooting of the universe.  Whatever plan the Incubators had, that wasn't it. 

I was basing my info on the PMMM wiki page for Kyubey, which has a section labeled: Speculation - The theories below have been proven right.
The specific entry indicated:
Spoiler [+]

• He also states that his/their reasons for creating magic girls is so that new cultures can arise without the heat death of the universe preventing that. He seems rather nonchalant about leaving Earth to be destroyed at the hands of Kriemhild Gretchen in timeline 4. Given that nearly all of the population dynamics models made for the Puella Magica world will inevitably result in the destruction of life on that planet and that Earth is clearly not the only world harvested by Kyubey's race, their reasoning seems rather suspect. Assuming they really are collecting the energy to stave off the heat death of the universe, for other cultures doesn't appear to be their reason for doing it. If he is consciously lying about the reason, then this would make his story to Madoka another attempt to manipulate her by claiming it's 'for the greater good.' Additionally, if this was the reason and if magic/wishes can really do anything, then why not simply explain it to someone and ask them to make a wish to prevent the universe from suffering heat death? Surely someone somewhere in the universe would be willing to make such a wish.
  

Confirmation: This is actually said. in the anime.

I have my doubts about some of that.

Spoiler

Does the anime actually state that they are harvesting additional worlds?  I don't recall that, and I don't put much faith in those population models, given that the system has not exploded in the last few thousand years, and the Incubators can act as a break if needed.  Remember, witches (Walpurgisnacht aside) are vulnerable to mundane weaponry, and their labyrinths won't stop Incubators from entering.  Also, going back and looking at the episodes, Kyubey says that they studied other races for compatibility with their emotions to energy technology, and that when they found humanity they were surprised by the range of emotions that humanity can experience, and that all humans experience emotions to that extent.  And given that they limited their harvesting to the most efficient subset of humanity, I doubt they harvested less efficient species as well.
Also, we don't know how they intended to use the collected energy to combat entropy.  All we know is that there is some finite amount of energy they require.  Perhaps they have invented some device that will counter the issue somehow, but it has a giant start up cost, and collecting the energy needed through normal means would result in more energy lost than is gathered, so they went looking for a source of "free" energy.  We don't know. 
As for wishing away entropy, I'd imagine that finding someone who has strong enough emotions on the subject to make a wish regarding it, and also has the absurd amounts of karmic weight that Madoka had so to be able to make a wish powerful enough to rewrite physics would be rather difficult.  This is made even more difficult because the Incubators don't truly understand emotion.  There's also the issue that, before Madoka, such a wish would also produce a witch with the power to destroy the universe.  The Incubators are the catalysts, but the actual power that grants the wish is that of the wisher.  (If it was just the Incubators granting the wishes, then that would mean that they could have rewritten the universe like Madoka did, at any time, which would have meant that the events in the show never would have happened.

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Stand between the Silver Crystal and the Golden Sea.
"Youngsters these days just have no appreciation for the magnificence of the legendary cucumber."  --Krityan Elder, Tales of Vesperia.