It does that now, but there is no guarantee that this consensus holds. Maybe it's quite likely that it holds, but nothing guarantees it.
> Full nodes are economic actors, such as people who sell goods and services, who fully verify the chain. They simply refuse accept inflated Bitcoin.
They can refuse to accept inflated Bitcoin, but somebody has to mine new blocks. If the vast majority of miners decide to do something, the remaining miners will have trouble mining new blocks and the entire system is heavily disrupted.
As you say, they are economic actors, so when faced with the decision of having a severe service disruption and giving in to miner demands, the choice may well be the latter. After all, why would they prefer to use a "original Bitcoin" that only has 1% of the hash rate? Because it has the original brand?
It's ironic that even modest monetary inflation is considered bad by so many Bitcoin proponents when that inflation is what pays for the Bitcoin network. Perhaps some day, transaction costs will make up for it, but that is not a given.
> A Bitcoin full (non-mining) node only takes 5GB storage space and 128MB RAM to run.
It's completely irrelevant how many non-mining nodes there are. The only thing that matters is who runs them (exchanges, merchants, actual users).
