The players of the campaign are expected to be heroes.
That's part of why they are referred to as heroes in the A:RPG instead of "characters," "adventurers," or "schmucks." But you're right. There is no "alignment" in this game and there are lots of (different) ways to define what a hero is. And I'm sure mileage on this point varies a lot. My definition, for what its worth, is: "a hero is someone who attempts to make dynamic progress against a real problem no one else has the ability or will to solve."
That leaves a lot of room to sometimes choose to do "dark" or "evil" things.
And there are no shortages of characters in fiction who are "heroes" who are not people you want dating a loved one... Michael Moorcocks's Elric is the poster child of this. You could also look at Jack Vance's Cudgel the Clever, the story of Gilgamesh or half a dozen characters from Game of Thrones. I believe you can be a heroes and do all kinds of bad stuff.
That said ...There was a guy in the old campaign who got a certed (heretical/cursed) Cloak of Eyes from a mod that featured the minions of the 1,000 Eyed Man. And that character openly showed up with said cloak at the first LARP set in King Osric's court (since it was grafted to his neck it was hard to leave behind
). I think the expectation was ... what's anyone going to do? And the answer was, execute the character. Choices have consequences. [There was a brief role play between the LLT who served the Inquisition and the Knights of the Kingdom over who had the right to execute him. The Knights prevailed. And that was the end of that character.] I want to add Henry talked to the guy first and explained what was going to happen and why, and that in Arcanis there are choices and consequences ... it wasn't like we just dragged the guy off into the corner, roughed him up and tore up his cert binder.
I don't think of myself as an adversarial GM, but I do expect a certain level of maturity from Arcanis players. If your character is doing dark things that "make sense" that's cool. Don't get caught by your enemies or authorities...you understand you're taking your own chances. If you're playing "a psycho" to act out...then as a judge I am (eventually) going to do something about it (as soon as a story appropriate "opportunity" arises).
I say all this, but really? In game play as a practical matter I don't think this comes up.