if a poor family is spending 90% of their income on day to day expenses, and a rich family is spending 20%, and there is 10% inflation, then the poor family will then be spending 99%, which is a 90% reduction in margin of safety/ability to invest. The rich family will then be spending 22% which is a 2.5% reduction in margin of safety/ability to invest.
Now, you might argue that wages catch up. For starters, many poor are on fixed incomes. BUT even for the employed, liberal economists routinely argue for screwing the poor out of their wages (of course they don't put it that way):
http://krugman.blogs.nytimes.com/2010/02/13/the-case-for-hig...
It goes like this: even in the long run, it’s really, really hard to cut nominal wages. Yet when you have very low inflation, getting relative wages right would require that a significant number of workers take wage cuts.
Think very carefully about what that means.
Ironically, it was keynes himself that warned:
By a continuing process of inflation, governments can confiscate, secretly and unobserved, an important part of the wealth of their citizens. By this method they not only confiscate, but they confiscate arbitrarily; and, while the process impoverishes many, it actually enriches some. The sight of this arbitrary rearrangement of riches strikes not only at security, but at confidence in the equity of the existing distribution of wealth. Those to whom the system brings windfalls, beyond their deserts and even beyond their expectations or desires, become 'profiteers,' who are the object of the hatred of the bourgeoisie, whom the inflationism has impoverished, not less than of the proletariat.