If you want to look at inflation as a tax, you have to view it as a tax on savings, not on material goods. Material goods prices should increase with inflation while your savings doesn't. This discourages saving. It drives demand up. In the opposite view, deflation has been one of the things that all economist fear most, as it decreases demand. Why buy a house if that house is going to be cheaper tomorrow?
Also you can't look at future obligations as how it would effect today. First future debt is hugely related to GDP growth which is extremely hard to predict and has continuosly proven the bears wrong on that aspect. Second, it has no effect on today. It is a tool to help plan for the future. Monetary base effects inflation, i.e. real dollars being spent in the economy right now. Not future dollars possibly being spent in the future effecting today.