The Eros-Thanatos thing that they were based on:
So this is a Freudian theory as we all probably know. Obviously it goes without saying that Freud was a cocaine-fueled misogynist whose ideas warped the popular social views about human nature for nearly a century, but nonetheless that's what they came from - a vague inspiration from a class that an 18 year old kid took in college. Further, the life-drive death-drive theory is considered one of Freud's weakest, and he was pretty much unable to make it consistent or solid. That of course in and of itself is interesting because real life is complex and real relationships change all the time, but basically the reason why it failed to stand on its own two feet was because of its dualistic nature! That is, when exposed to further analysis, his "Eros and Thanatos" concepts turn out to not be in opposition to each other, but actually collapse into each other/use each other/have elements of each other
in each other.
That's awesome. Why hasn't that ever been explored?
So even though "Eros" is usually translated as 'sex drive' so seems kind of base, it's actually the drive for love in its entirety. (And it's important to note that the life-drive Eros is
not Freud's famous Pleasure Principle, actually, even though that's kind of the direction Eros was taken in.) But it's motivated by Thanatos and cannot
exist without Thanatos because it is a
reaction to Thanatos. And technically in the same way, the Thanatos too cannot be seen without the Eros.
You don't see this in the comics with the brothers because Warlock kind of took on Eros's role there, but in my opinion Warlock's yin-yang constituent parts nullify the allegory there - besides, there's a very important difference between the way Thanos and Warlock are done, which
is more yin-yang, and the concept of Thanatos and
Eros: In the Freudian concept of Thanatos and Eros, Thanatos is more fundamental, powerful and influential than the Eros drive. Eros is constantly motivated and influenced by Thanatos. Thanatos, on the other hand, is not affected by Eros at all. Not even one iota. It exists as it is regardless.
Like how no matter what we do in life, and how lively we are, and how little we think about it or how desperately we try to ignore it, our inevitable death looms silently in the background.
This is cool, why haven't they done anything with it???
But they of course also collapse into each other in other ways: aggressive violence (Thanatos) being displayed for self-preservation or defending people you love (Eros). And in the comics, of course (though now with Revelation it's kind of a moot point), with the way Thanos loves Death, that's literally the definition of Eros, while his vitriol and anger towards her for not returning the feelings as well as his base desire to cause pain and suffering and death
regardless - and iirc for Thanos it really is, like, an
urge - well, that's the Thanatos part.
tl;dr while Freud tried to make the life-urge (Eros) and death-drive (Thanatos) dualistic, equal opposites, he couldn't figure out how, because they're actually kind of jumbled, and the relationship between them is unequal and they sometimes blend together: Eros is influenced by/is a reaction to Thanatos and is unable to influence Thanatos in return; the love of life is just a manifestation of the fear of death etc. This is cool and should have gone somewhere.
lol you can read some more about the life urge and death urge here if you're also crazy