“And, yes, such a ban can also be applied to baking yeast, if that is an issue.”
Could they ban water, sugar, and grains too? Because all are also used to make alcohol.
The key is whether it is causing a problem or not. Vegemite is currently causing a problem in some communities, which is why this issue has come up. Nobody is claiming at the moment that general access to grains or sugar or anything like that is a problem.
This is very unlikely to happen anyway but if it did it would be because the local authorities (the elders of particular Aboriginal communities in essence) had identified a specific problem which they thought a ban would help with, and they asked the government to take action to help them enforce such a ban. It’s not a blunt instrument approach, it’s targeted based on the problems that are occurring, not problems that theoretically might occur in the future.