This number is indeed arbitrary. Sure, the higher the inflation rate, the better for stakers, but with delegated proof of stake, I tend to believe anyone that will plan to hold will be staking (thanks to these businesses such as chainomatic). Only those needing access for purchase (spending account) will have non-staking tezzies.
But on the other hand, it sends a cold shower to anyone interested in Tezos once they learn about a high inflation rate (the general public only knows about Bitcoin and somewhat less Ethereum). In my opinion, I would make it 2% to fit with this “ECB mandated 2% inflation rate” Bovine Excrement that they have in their mandate. We know very well that in reality, the European Central Bank is talking about price inflation without consideration for asset inflation (ie: it’s not the inflation of the currency supply but price inflation they are talking about) - so in reality they had a higher rate, but that’s beside the point since the public don’t think or know about these details.
It’s all about public perception. One of the attraction of Bitcoin to many is to know it has a hard limit of 21 million bitcoins, even though that will not be reached until about 2140.
Alternatively, we very likely should not have it at 0% since then not as many might care to stake (only transactions fees as reward). The security of the Tezos network will be stronger with a higher number of nodes staking, hence the incentive to stake so not to lose.