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He held the rank of Jedi, but the Jedi Council were jealous and didn’t give Anakin what he deserved.
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He saw visions of his wife dying and was willing to do anything to save her, yes, including killing kids. This isn’t evil; this is true love.
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After he became Vader, he found out his wife died.
Justifiable crash-out, to be honest
Humans will readily disregard the humanity of vast classes of other humans. It’s especially easy to do it when those people are in fact fictional, but I think it’s the exact same mechanism. They just don’t extend humanity to those people.
While watching Dr Strange 2, I was very confident Wanda wouldn’t kill Wong. Why? Because the audience would be less likely to forgive her for killing an important character. Killing extras doesn’t hit the audience the same way emotionally. Audiences will forgive a morally grey character for mass murder more readily than the murder of a character we’ve gotten to know.