I haven't seen any evidence that convinces me that modest inflation causes people to spend money sooner (If you have any I would be very interested to see it).
I think that easy access to credit definitely affects people's spending behavior, but I don't have a lot of data to back that up.
You can't have it both ways: either inflation (of a certain rate) is good because it makes people spend sooner, or it doesn't change behavior.
Edit: or there's some other way in which you operationalize the goal of "increased economic activity" that's orthogonal to "spending earnings sooner than you otherwise would".
By spending I intended "purchasing depreciating (or disposable) assets"
Purchasing equities as an inflation hedge is not what I meant. Inflation does encourage riskier investments, as merely holding currency is insufficient to maintain capital.
I agree that it's an open question whether or not that's a good thing: some would argue that encouraging riskier investments encourages malinvestments which becomes a net negative; others argue that the increased activity caused by risky investments outweighs the damage done by malinvestments; I've even run into many who claim that even malinvestments are good, since moving money around is good no matter the reason.
If that last point of view is true, I'm giving up on economics, but the first two both seem reasonable to me.
And yes, there are trade offs, one of which is the malinvestments from spurring people to hold non cash. My point was that this, plus the individual welfare loss of the hoarder from having to commit to purchase sooner, must be weighed against the purported benefits of (what you got people to do via) inflation -- and (as I said at the beginning) that most people who make that argument for inflation (even economists) don't offer a way of modeling those relative benefits.
It's like arguing for an apple subsidy on the basis that apples are good, without even thinking about the costs of such a subsidy (ie diversion from non-apple production).
When someone proposes n% inflation as a way of "taxing" hoarding, what's the corresponding model? What's the "rising sea level" there?
In cases of a ~100% "inflation tax" (aka hyperinflation), we see the harms clearly: people have to spend money almost the second they get it. They have to move up purchases and otherwise arrange their lives in ways that are extremely welfare harming, and which probably outweigh the benefits of the greater economic activity it induces.
(Contrary to a lot of talk on hyperinflation, I don't see the chief problem as being volatility; even with stable, predictable hyperinflation you have the problem of losing the main benefit of money, which is that you don't have to know what you'll ultimately be buying in order to produce something for sale.)
So likewise, to justify a Pigovian argument for inflation, you would likewise need a model, or otherwise gauge the magnitude, of the "costs of making people move up purchases [when they'd rather save and decide later]" -- the costs that become extreme in the case of hyperinflation. And yet virtually everyone enamored of the "we need to encourage economic activity" argument for activity has nothing in the way of this. Hence my frustration with it.
(The analog of hyperinflation in carbon taxes would be a ban, or absurdly high tax, on burning of fossil fuels, and has the corresponding welfare harm that the avoided fuel usage -- or costs in evading the ban -- far exceed the welfare harm of the emissions themselves.)