Without using parentheses, the only thing you can use to rationalize why you don't group the 2 and the 12 is a left to right direction.
So if we can agree that in fact it is the left to right rule that makes this expression unambiguous, then you have to contend with the fact that said rule is not taught everywhere in America, and seems not to be taught at all in certain other countries - which leaves us with a situation of true ambiguity. This should not come as a big surprise: the controversy is probably raging for a reason.
As a side note, when written as:
48 / 2 x 12
... the left to right order is so intuitive that you would be forgiven for overlooking the need for it to be codified in a rule.
However when written as:
48 / 2(9+3)
It is no longer intuitive at all because we start from the right, evaluating the parentheses first, then have a natural tendency to want to multiply the contents of the parentheses - a tendency exacerbated for people who use programming or scripting languages.
Anyway, that is really a side note because we both agree that we should not be relying on intuition for such things - there needs to be clear cut and unambiguously defined, coherent rules. So either there is a left to right rule or there is not. If there is not, then you have not provided a reason for why 48 / 2 x 12 is unambiguous.