With a few exceptions like devils and demons, this concept doesn't exist when I run. Some creatures will start hostile, some won't. But few are inherently good or evil that they can just be murderhobo'd off.
I've had plenty of encounters turn into talking that I hadn't expected, plenty turn into combat where I hadn't expected.
Now, there can be consequences. Kill a merchant and you might find yourself ostracized with a bounty on your head if someone notices. Same is true if it's in an elven tree-city, an isolated halfling village, a drow metropolis, or a hobgoblin trading post.
