OK, so you don't want to consider Saville's findings of an incident when UK forces fulfilled their oath, followed orders and shot dead unarmed civilians. I can appreciate why you would seek to dodge that.
My "cohesive argument" appears to be one that you find challenging. Those swearing the oath are committed to follow all orders, and you insist that you would not follow what you consider to be illegal ones. I'll ask again; is it actually illegal to down a passenger jet failing to respond to warnings; is it illegal to fire upon unarmed civilians breaking down the gates of Buckingham Palace and is it illegal to strike-break?
I suggest you read, alongside the oath, Queens' regulations, and the British Army's standard RoE.
What you
should be asking, but seemingly won't (perhaps you have antipathy toward the military?) is: "Is it legal for a pilot to refuse to shoot down a passenger jet/fire upon unarmed civilians/strike-break?". If you did, you might get constructive answers.
The answers, by the way, are:
1) Yes, it's legal for a pilot to refuse such an order (although it's also the case that pilots are trained to depersonalise what they do, which makes them more liable to carry out their mission regardless of legality - that and because they're floppy-haired cunts).
2) It's legal for a soldier to refuse to open fire on unarmed civilians. There's a measure of "proportionate response" expected in orders, so an officer issuing such an order if there were no imminent threat wouldn't be acting within the boundaries of their responsibilities.
3) It's legal for a soldier to strike-break
if, and only if, the strike-break threatens lives and safety, hence the breaking of fire strikes. The use of soldiers in the various large-scale strikes in the first half of the 20th century, while not illegal, was certainly a misuse of manpower, and an illustration of just how interlinked the Establishment and the military were.
Do you actually know the definitive answers to these orders that a service-person would have sworn to follow?
Given the legal system there
aren't "definitive" answers, only what happens case by case, and the applicability of a "conscience clause" to the actions of an individual.