To me a bouncer pulling a short sword is not a bouncer doing their job. They just transitioned from bouncer to attempted murderer. A short sword is not a weapon of subdual. If he pulled out a club or baton sure, but not a short sword. That's the modern equivalent of a bouncer pulling out a 9mm pistol and shooting at the PCs. Only instead of being outmatched he runs out of bullets and then surrenders.
Now the campaign comes into play. Is this an old west style where if someone tries to kill you it's ok to kill them? Is the law of the land such that trying to kill someone is punishible by death? Are the PCs allowed to meet out justice? Depending on personal, religious, and social laws a paladin or cleric of a god of justice may be well within their rights and religious tenants or oaths of justice to execute the person. What happens when next time the bouncer pulls his sword in a brawl but doesn't face a highly skilled opponent and kills a couple of people? Do the PCs rest easy knowing that they took the moral high ground even though little Timmy doesn't have a dad anymore and his family is going to be out on the streets where they'll starve and die because they can't farm the land? Is one of the PCs a noble and required to uphold the social order by executing someone who dared raise a weapon against nobility?
There are so many pieces of information that we don't have that can easily make this not "cold blooded murder" that so many are jumping to.
NPC: "You slaughtered everyone in the wordworkers guild!"
PC: "Yeah, but they were all bad."
NPC: "Oh, that's ok then. Here is your reward."
vs
NPC: "You killed the bouncer at the tavern!"
PC: He drew his sword and tried to kill me."
NPC: "We don't care! It's cold blooded murder!!11one Sick the entire world on him!!"
edit:
I had to add this (warning, language)
http://terminallance.com/2011/08/12/terminal-lance-140-escalation-of-force/