If you hold that charging interest is immoral, then why not inflation?
I am afraid I do not believe that inflation has anything to do with morality. Actually, inflation takes its effects because of the market forces. An increasing gap between the extent of demand and supply will translate into inflation. The government needs to take steps to ensure that there remains a healthy balance between the purchasing power of the citizens and the availability of commodities in markets. As you see, there is nothing immoral as regards inflation though it is a problem ensued as a result of mismanagement. Just as improper supply of water to a region would not be termed as immoral rather a product of mismanagement—which if done on purpose is indeed a crime, inflation in itself cannot be termed as ‘immoral’.