Most economists agree that sales taxes are the fairest because they are always proportional to consumption.

I don't get it - what about "taxing consumption" makes it "fair"? Poor people aren't poor because they spend more money than others. They are poor because they don't have enough money to live a "decent" life (assume a middle-class lifestyle) or to even save it. Right?

Until you get to things like Vimes Theory of Boots. Not all consumption is equal. Not all consumption can be reduced. A burger wrapper might not care about economic status, the bag of beans and rice might.

How is reducibility relevant?

Do you think the burger wrapper just automatically winks out of existence for poor people?

Again, what has that got to do with the "fairness" aspect of taxing consumption?

There are no “fairness” molecules so it clearly cannot be relevant for the physical generation of negative externalities.

How exactly that load is divvied up by society, where it would apply, is not something I know the answer to.

i thought most economists would agree that consumption should be encouraged and savings should be discouraged. and that'd be how progressive taxes work? people tend to save more and consume less as their incomes increase?

Citation required.

The economists I've read disagree strongly.