I think it is pretty common knowledge that money has diminishing returns. What I find absurd is that people actually bought the trickle-down nonsense. It's almost on the same level as flat earth. It's sooo obvious that this isn't how the economy works.
If you want to give money away, give it to those who actually need it not those who need it least.
I don't think it's that simple. In a setting where there is little concentration of wealth, and where it is also hard or impossible to borrow money for productive purposes, I can easily imagine giving money to the "supply side" leading to large gains that "lift all boats" compared to not giving that money.
With the benefit of hindsight, I don't think we've been in a situation that resembles that (at least in the US) at any point since "supply side economics" was formulated. I don't know what I would have thought at the time; I expect it was less obvious than it feels now.
There's remains the possibility that, even in a situation like that, some other approach would work even better, although naively pumping money into the "demand side" probably isn't that approach.
“trickle down” wasn't what proponents called it, it's something a comedian called it derogatorily that stuck.
Ditto “voodoo economics”, except the critic wasn't a comedian, but a politician (of the party that rejected the criticism and went whole hog on the policy, but still later nominated him as, and got him elected, President.)
