You had your Session Zero, and talked about the play expectations, right?
Yes, and my play expectations are very open-ended and more or less come down to anything goes. I'll argue against restrictions that aren't setting-based, other than a very few clear no-go areas e.g. sexual assault, even if those restrictions aren't going to apply to me: for example if my character idea is a goody-two-shoes knight in shining armour I'll still argue against banning evil PCs.
If that didn't include killing shopkeepers as the way to make their living, then no, the GM is not obligated to support it.
I disagree. When I DM (which I do about half the time) I run the game/setting for the players to play in and, to a large extent, do what they want with. Their characters are their own to play as they please. As such, it's simply part of my job as DM to hit whatever curveballs they throw at me at such times* as they decide to throw them.
As a player, I feel justified in expecting the same of that game's DM.
* - sometimes I'll go years between having to hit a curveball, other times they come fast and furious.