I think the concern is justified. However, considering Japan during the 90s and the Great Depression makes deflation appear much more dangerous and persistent than inflation because no one knows how to fight it once it's become entrenched.

We know how to fight inflation. Interest rates can be raised without limit. They cannot fall without limit. The Fed can sell the bonds they are now buying back into the market and thus reduce money supply.

And you need to consider two other facts. First, the monetary base you plotted is just a small fraction of overall money supply (M1, M2, M3). Other parts of the money supply are growing as well but not as fast. Second, money that isn't used has no effect on inflation. The speed of circulation is sharply reduced in recessionary times and that's why the amount of money has to be sharply increased to counteract that potential deflationary spiral.

The line you want to plot is the amount of all monies (the Ms) normalized over the speed of circulation. That line is flat to falling, but it's true that there is a potential for a sharp rise down the road.

Inflation is very likely in say two years time. It's very difficult, politically, to raise interest rates while unemployment is still high. And inflating debt away is rather convenient for a heavily indebted nation like the US as well.