Tell me, if you take no oath and according to international law, no country can force you into citizenship, what would that make you?
Get over the hypotheticals, it has nothing to do with citizenship at birth.
The example of the navy ship in Canadian waters; you are a Canadian citizen by birth, per Canadian law. Even if you were born on a US Navy vessel to two US citizens.
Canada grants you citizenship; it is up to you to claim it, but you are a citizen as far as Canada is concerned nevertheless.
That is not hypothetical, that is real. Is your concern over dual citizenship or not?