Being shot at, and possibly killed, is a known hazard for anyone who chooses to take up arms.
That is exactly why we (the Merchant Navy) dont want to be armed. Your argument was good up until you contadicted yourself.
You write like an Australian, in which case check your own government rules about armed vessels, even Navy vessel have to jump through hoops, getting a merchant vessel in would be even worse.
Add to this that international shipping is just that, how do you control who as the arms? Every vessel would be entitled to carry arms including those carrying people who at present most countries call terrorists, so lets make life easier for them give them the arms they require legally there isnt an administration on the planet that would alow that.