Warning: contains spoilers for Eternals #6!
While Thanos is one of Marvel's most brutal villains, he's also one of the most brilliant - a warrior-scientist and philosopher as capable of ending lives with his mind as his fists. Because of this, Thanos' motives are often cosmic in scope. While Josh Brolin's MCU depiction of the character was focused on universal balance, killing off half of all life in order to safeguard resources for the rest (a plan many have since pointed out has some major logical flaws), the comic version of the Mad Titan has traditionally been obsessed with courting the metaphysical representation of Death, but even that isn't the whole truth, and Eternals #6 makes it clear there's a more visceral reason that Thanos causes so much carnage.
The truth that so many of Thanos' stories arrive at is that he doesn't kill others simply because he loves the goddess-like expression of Death, but instead that his love for Death is an extension of his obsession with ending life. A true nihilist, Thanos considers life devoid of purpose, making it his personal mission to end what he sees as an empty pageant. But this quest isn't simply about winning a unique place in Death's heart or earning oblivion for himself - it's about enacting the philosophy that has dominated his life.
In Eternals #6, fans see how Thanos returned to life after his botched resurrection by Hela. The Eternal Phastos resurrected Thanos to destroy the Great Machine, fitting him with specially designed synthetic internal organs in order to keep him under control. The Great Machine - an expression of Earth's consciousness - narrates Thanos' return to consciousness, recounting his first thoughts on awakening. "He breathes deeply and swears vengeance at all who have done him wrong... All who breathe do him wrong by continuing to exist." While Thanos is temporarily defeated by the Eternals this issue, the reveal that he doesn't just seek or wish to honor Death - but rather feels personally wronged by all life - makes it clear how deep Thanos' dark philosophy goes.
Part of Thanos' rage is his inability to die. Past stories have described Thanos as being effectively allergic to life, suffering every moment he exists, but even on those occasions where he's obtained supreme power, Thanos has always chosen to kill others rather than erase himself from existence. Having observed every living being on Earth for the entirety of their existence, and being intimately connected to every Eternal (a categorization that the series confirms includes Thanos), the Great Machine is the most authoritative source ever to describe the Mad Titan's beliefs, and it makes it clear that he feels personally attacked by all who live, viewing his deadly actions as "vengeance" on those who have already wronged him.
Like any Marvel character, Thanos has been depicted by countless writers and artists, deviating significantly from the original vision of creator Jim Starlin. But the version of Thanos in Eternals #6 - from Kieron Gillen, Esad Ribic, and Matthew Wilson - is one of the most fascinating yet. Rather than a simple lovesick killer willing to destroy others in tribute to his goddess, this Thanos is a true believer so absolute in his disdain for life that he views killing as an act of vengeance. This Thanos feels so oppressed by existence that even after killing half of all life, he doesn't consider himself the aggressor.
It's a reading of Thanos that helps make sense of some of his more striking acts of genocide, committing him not just to escaping life or pleasing Death, but waging war on a universe that has brought him nothing but pain. Marketing materials for Eternals #7 and Eternals: Thanos Rises #1 have made it clear this iteration of Thanos isn't going anywhere soon, giving Marvel the opportunity to dig even deeper into the Mad Titan's motivations and explore the twisted ideology that regards all life as an insult that must be answered in kind.