Which missionary efforts? If you mean paying Zakat to those whose hearts are inclined toward Islam that's something different.
> a tax on harvests
I mentioned this in my previous post. Livestock and produce have different Zakat calculations than the 2.5% of money held for a year.
If you're referring to Ushr, that's imposed on non-Muslim nations that taxed Muslims, so a tit-for-tat treatment, and it's not part of Islam per-se, but a socio-political decision.
> certainly that intentionally engineered by the central bank
Exactly what we don't want. We don't want a select few people to determine the tax rate for the entire population, affecting mainly people at the lower socioeconomic levels in society.