The argument against helicopter money as a means of boosting aggregate demand is it is inflationary.
Not necessarily if the velocity of money increases and there is an output gap.
A thought experiment though imagine there was no guarantee of this.
Monetary financing would deflate the value of a currency against other currencies and increase input prices – leading to at least short run cost plus inflation.
But what if every currency did this?
If there was an even balance of trade between each country there would eb no inflation – the effects would cancel. This is I think the thinking behind Hawtrys monetary parable of ships racing to port in a storm – the argument being if you are in a storm you get there as quickly as possible.