Interesting discussion guys: Why remove the gun when it has intrinisic value, especially in their line of business. Besides the logistics of a gun being mounted outside I think there is something more fundamental here.
There is a specific choice being made here which isn’t in alignment with the character’s actions. Everyone is packing heat or has held a gun or in the movie, so they are not making a point of pacifism. Mal kicks guys into the engine and shoots unarmed Alliance officers. Yet they make a specific point about showing us they remove the gun from the ship. Why? Badger has already spoke to it: Serenity is not a ship. It is their home. Two quotes and a definition help flesh this out from Out of Gas:
MAL: I tell ya, Zoe, we find ourselves a mechanic, get her running again. Hire a good pilot. Maybe even a cook. Live like real people. Small crew, them as feel the need to be free. Take jobs as they come – and we’ll never be under the heel of nobody ever again. No matter how long the arm of the Alliance might get, we’ll just get ourselves a little further.
SALESMAN: I tell you what, you buy this ship, treat her proper,
she’ll be with ya for the rest of your life.
Definition of the word “Serenity”: the state or quality of being serene, calm, or tranquil; sereneness.
Mal purchases the ship as a reaction to the war, a war he fought in as a volunteer on the side of those wanted to live free. The side he fought for abandoned the fight leaving him flapping. The purpose of the ship isn’t trade, or smuggling or fighting, its purpose is freedom. If his purpose is survival he finds himself on the same path of the ship that finds Serenity adrift lacking a catalsyer and shoots Mal as a means to an end. He could arm himself to the teeth and the only thing that would accomplish is escalation and becoming something he is not: a brute and a thief. He is neither…at least his image of himself is not. Serenity is the personification of his view of the man he wants to be, the jobs he takes are simply his way of accompishing his goal: Be free.