Bad Guys Doing Good Things

Question: Considering that the Aztecs thought that the stars were evil, why did they worship Mixcoatl?

The Aztec worldview, which it's easy to distill it down to "sun good, stars bad", is actually a very complex one. Just as some of the Greek Titans were worshiped alongside the gods as deities themselves, so were the Aztec "Titans" considered gods as well, tasked with managing parts of the universe to keep everything running smoothly. Not just Mixcoatl but also Coatlicue and Itzpapalotl were major figures with their own centers of worship; they weren't always pleasant, but, like all Aztec gods, they were still considered entirely necessary.

To the ancient Aztecs, the universe was created and supported by the gods and required constant maintenance by them to avoid collapsing. The purpose of blood sacrifice and worship was to feed these gods enough energy to go on maintaining everything - and that means everything, from happy butterflies and pretty girls to the awesome powers of the sun to the terrible dangers of the night. Stars are part of the Fifth World, howsoever much they are usually associated with scary and dangerous things, and therefore they need to be maintained as much as everything else. Mixcoatl is the guy who does that maintaining, as patron of the Milky Way and father of the morning and evening stars; without him, that part of the world might break down, and above all the Aztecs do not want any parts of the world breaking down.

The stars - the night sky in general, in fact - often have negative connotations in Aztec myth, but that doesn't necessarily mean all things associated with them are evil. The tzitzimime, terrible star-demons that devour women and children and rain ill luck down on the world, are one of the great bogeymen of the Aztec culture, but Quetzalcoatl acting as the morning star is a positive light in the darkness. And there are also figures like Tezcatlipoca, both a patron of the night and a supporter of the Aztec empire, a figure to be feared and a god to be worshiped. This isn't contradictory; it's just a good example of the fact that the ancient Aztec religion was not always black and white, and that some things, places and people might be simultaneously good or necessary for humanity but also dangerous or horrible to deal with.

While we often talk about Mixcoatl as the big daddy of the stars (because, well, he is), it's not the only thing he does. He's also the major patron god of hunting, making him the figure most worshiped by warriors and hunters who wanted his blessings and hoped to emulate him. Most of his festivals and dedications have to do with this hunting aspect of his persona; it's the part of his personality that most directly benefits humanity and is certainly less ambiguous than his role as patron of the stars, so (for the star-phobic Mexica, at least) it was mostly his hunting prowess that won him respect and worship. Sacrifices to Mixcoatl ensured continuing supplies of game, good hunting and enough food for the community, important for a people who spent a lot of their time as nomadic wanderers before settling in at Tenochtitlan.

Finally, it's also important to remember that Mixcoatl isn't a purely Aztec god; he predates the rise of Tenochtitlan and was worshiped in various other ancient Mexican civilizations before being absorbed into the Aztec pantheon. Some of those cultures aren't as worried about stars as the Aztecs; others considered Mixcoatl their supreme patron, making it hard to completely get rid of him in much of the empire even after Huitzilopochtli had taken his place as the preeminent god. My favorite example is the Toltec city of Culhacan; the Codex Chimalpopoca contains a particularly amusing story in which the Culhua relate that they knew that the Mexica were coming to conquer them and indeed got thoroughly conquered, but that the Mexica, in their quest to capture the cult statue of Mixcoatl and take it back to their capital, actually took the wrong one because they weren't as familiar with him as the natives. Classic Mesoamerican hijinks.

But really, as far as the worship of deities associated with scary or bad things goes, that's something that happens worldwide for various reasons. Gods are multifaceted, complicated beings who can rarely be accurately distilled down to simply Evil; the cultures who invented them are equally complex and usually attach many layers of symbolism and behavior to their deities.