History shows that flexible inflation rates have a nasty habit of changing regularly. This is generally done for the benefit of one group and at the expense of another. Bitcoin has a model and that model should be adhered to. There are altchains available with different philosophies at their cores, if one of those is seen as superior then free market forces should cause it to rise to prominence.
I don't think he was proposing a flexible inflation rate, but a fixed rate of around 1%. The fact is that every time someone accidentally deletes or loses their wallet, or someone passes away and no one uses their coins, or people abandon wallets with small fractions of coins that they consider worthless, that is all coins coming out of the system. When coins stops being added (again, not that we have to worry about this anytime soon), it could eventually reduce the amount of coins enough that the value of the remaining coins would be too high for average or below average consumers.