I've read the lore on the avian page on the wiki, and i've read the whole thing here: http://playstarbound.com/wp-content/uploads/2013/02/avianlore_pdf.pdf What I don't understand is how Stargazers are evil. I understand they're against Kleux, but when did they become hostile to just about everyone? Even the intro page when you start a new game as Avian says you escaped from the Stargazers like they're a bunch of Romulans. Do they make up the majority of the Avians? Because that's what I've figured from the pdf. If so then that would mean that starting as an Avian character would be a Kleux worshipper.
I think the Stargazers still worship Kluex, because it says (maybe?) that they established temples on the planets they found. Merueruer. -Shrug-
The stargazers control the main Avian government and temple (from what I understand). They wrestled control from the Loyalist government (the only real difference I can see from Loyalist and Stargazer is that Loyalist never wanted to leave their home system). The Grounded are a growing rebel movement that rejects the worship of Kluex. I'm not sure the Stargazers are hostile toward everyone. I'm pretty sure they're hostile toward Florans, because they've tried to blockade them on their homeworld. They're allied with the Glitch government it seems. It doesn't say much about their relationship with everyone else.
Stargazers are hostile toward everyone in-game for the same reason the USCM is hostile toward everyone; AI limitations. The Stargazers are the current dominant political and religious faction on Avos; as Roskii said, they seized power from a rival, xenophobic "Loyalist" party long ago. AS you may have guessed from their name, the Stargazers are big on science and exploration. However, being traditionalist avians, they're also big on theocracy. While vague, the game suggests the Stargazers to be something of a mix of the Illuminati, the KGBird, and the medieval Church in style. They are evil in so far as they practice the traditional rite of sacrifice, and are a bit zealous in their pursuit of the atheist Grounded. Given the majority of players play Grounded outcasts, it's only natural that the all-seeing, theocratic establishment will appear the villain.