In Infinity War, Thanos - despite his rhetoric centered on randomness - proves that he is irredeemably evil by murdering the innocent Asgardians.
Avengers: Infinity War depicts Thanos to be a genocidal fiend, but despite his popularity - and the MCU fans who claimed he had a point - the movie proves he is irredeemably evil. Throughout the planet-hopping superhero crossover, the Mad Titan tries again and again to justify his desire to wipe out half the universe's population, but his actions tell a far less altruistic story.
Thanos' repeated rhetoric centers around his impassioned belief that he must be the one to bring balance to the failing universe. His homeworld Titan fell victim to overpopulation and found itself with limited resources and though the warlord suggested the random decimation of half of its citizens to spare the planet, his ideas fell on deaf ears. After the doomed world eventually crumbled, Thanos pursued the Infinity Stones, in the hop of using them to prevent such an event from occurring on a universal scale. He further explains his reasoning to his daughter Gamora, telling her, rather practically, that "if life is left unchecked, life will cease to exist. It needs correction." That reasoning led to a movement in the wake of Infinity War's release that espoused him as somehow wise, despite his killing on such a huge scale.
It didn't help that a promotional trailer (released prior to Avengers: Infinity War's debut) depicted Josh Brolin's Thanos as seeming to enjoy himself during his acts of violence. With a voiceover delivered with a hint of malicious glee, Thanos growls,"Fun isn't something one considers when balancing the universe. But this... does put a smile on my face." While the line never made it into the final cut of the film, it does point to a certain joy found in the destruction, which is also consistent with the probably thousands of unnecessary deaths committed at the hands of the aptly named Mad Titan on his quest for "balance".
What Thanos might qualify as a "necessary" death may be a bit complicated. Obviously, there are the victims of Infinity Gauntlet's Snap themselves, whose demise would be required for the completion of his mission. Since his plan hinges on the acquisition of the Infinity Stones, he may be able to justify the deaths of those who stand in his way of obtaining them (i.e. Loki, Gamora, and Vision). However, there is another group of victims who are rarely discussed when considering the Mad Titan's many crimes: roughly half of the Asgardian population - with many innocent civilians among them. Going against his own claims of "randomness," Thanos specifically targets the Asgardians - of whom the survivors will presumably also be subject to the Snap, thus obliterating their numbers even further. That flies in the face of suggestions that Thanos is a more complex villain - like Killmonger or Zemo - who is merely misunderstood and destroys the logic of the Titan's vulgar fan club.
The creative decision to have Avengers: Infinity War begin in medias res after this bloody act has occurred may speak to the difficult balancing act of keeping Thanos both threatening and relatable - a challenge overcome, in part, by Josh Brolin's disarmingly charismatic performance. With the omission of a bloody event that might make the character less redeemable and harder to relate to, it also makes for a seemingly more practical (and less vindictive) antagonist. Yet, in Avengers: Endgame's final battle, a younger time-displaced Thanos angrily shouts, "I will shred this universe down to its last atom and... create a new one teeming with life that knows not what it has lost but only what it has been given. A grateful universe." The threat indicates the villain's disregard of his own stated desire for randomness and equality in favor of constructing a universe in which he is judge, jury, and executioner. Similarly, the innocent Asgardians suffered at Thanos' hands not because he deemed it fair, but because his emotions (and inherent evil) willed it so.
Thanos is often regarded as one of the MCU's most compelling villains to date, however, since he is used as the point-of-view character in the Avengers: Infinity War (a smart decision given the film's overpopulation with familiar heroes), the creators often obscure his darker intentions to make him more relatable. And, who knows, perhaps the Mad Titan has even deluded himself into believing his own rhetoric. Regardless, his cruel and inequitable violence toward the Asgardians is proof that, for a figure so preoccupied with "balance," Thanos consistently tips the scales too far in the wrong direction.