Why Vision Didn't Kill Thanos The Same Way Ultron Did In 'What If..?'

In it's penultimate episode, 'What If.. Ultron Won?', Marvel's What If..? provided a twist on its usual formula. For the first time, the episode's story, involving Ultron threatening the safety of the multiverse after obtaining all six Infinity Stones, will continue into next week's first season finale of the series. One rather shocking scene saw Ultron, in posession of the Mind Stone after successfully uploading himself into the body that became The Vision in the main MCU reality, slice Thanos in half with a single energy beam from the stone, thereafter claiming the other five stones for himself.

The scene has left many fans wondering why Vision did not dispense with Thanos the same way back in Infinity War. In theory, there's no hard and fast reason why he couldn't have. However, looking into certain plot points in the film, and Vision as a character, there's probably a few reasons why he didn't.

Vision was seriously injured for most of Infinity War

As fans are well aware, Vision is seriously injured early in Avengers: Infinity War, after being stabbed through the back by Corvus Glaive in an ambush on himself and Wanda Maximoff. The injury takes most of Vision's most useful abilities, including phasing and changing his density, out of commission. The loss of his density altering abilities also leaves Vision struggling to fly, which forces the Scarlet Witch to carry him with her powers during their attempts to escape Glaive and the other Children of Thanos.

We know that Vision's injury doesn't stop him from using the Mind Stone's beam entirely, as he uses it at least twice in the film, first after Glaive threatens Wanda's life, and later while attempting to protect Princess Shuri in Wakanda. However, in his damaged state, using the stone likely took more out of him than it usually would, and by the time Thanos arrives, Vision has been damaged further in battle.

Vision has always tightly controlled his use of the Mind Stone as a weapon

While the Mind Stone beam is the strongest of the offensive abilities Vision possesses, he rarely uses it except in dire moments. In Age of Ultron he uses it only when the Avengers are deep in the thick of battle against the Ultron army, most notably in a memorable shot in which he is aiding Thor and Iron Man against a particularly stubborn drone, and later, to take out the final Ultron, while alone with it in the forest, where no-one else is around to be harmed. In Civil War, he uses it at very low power to free himself from Clint's stun arrow, and later to try and prevent Team Cap's escape from the Airport. The only times Vision has turned the Stone's beam directly on an actual living being are the earlier mentioned attacks on Corvus Glaive.

Vision has always been respectful of the Mind Stone and the potential dangers it poses. It is also possible that Vision limited his use of the stone further out of guilt over injuring War Machine.

Vision is on the side of life

As he says soon after his birth in Age of Ultron, Vision is on the side of life. Killing would never be his first choice when ending a conflict if there were any other way. While Ultron's first instinct in What If..? was to kill Thanos upon his arrival, Vision may not have thought the same way. His first instinct was to preserve the other lives he had sort to protect, by ending his own life through the destruction of the Mind Stone, if necessary. He wouldn't have wanted to risk lives by striking at Thanos himself first, with the high likelihood that such a strike would fail in his weakened state.

There are probably quite a few reasons why Vision didn't kill Thanos in the fashion of What If's? Ultron. However, the most likely reason is that Vision is a much different, more altruistic character than Ultron, and after seeing what an Ultron with the stones is like, we're very lucky that he was.