Simple Math

The concept of supply side economics is actually quite simple.  If you reduce the cost to suppliers, they will reduce the cost to consumers.  Consumers will then buy more requiring the suppliers to hire more people.  This increases disposable income leading to more consumption, more hiring, etc. etc.  The increased economic activity will replace any lost taxes since while everyone is paying a lower percentage, the total pie is so much bigger.

Now the logic is really the same as a pyramid scheme and the ultimate issue with a pyramid scheme is that the number of potential members is ultimately limited.  When a pyramid runs out of new members it can't pay the latest members and it starts to collapse.

Supply side economics is limited by the amount of consumption that can be created.  Take a commodity like oil.  We've seen oil prices plunge based on a supply glut.  This has resulted in some increase in consumption but not enough to bring the prices back up.  Maybe over a longer cycle, if people were convinced that oil would stay cheap they might design additional uses for it into products, but that isn't easy or even likely since the market is volatile.  The reaction has been a decrease in non-competitive oil production leading to reverses in economic booms in some states and countries.

There is no such thing as unlimited consumption.  Supply side can be used when there is untapped consumption and unused capacity to absorb the increased output and provide jobs for underutilized employees.  However in the absence of those two things it creates something of a bubble, and increases the deficit in two ways.

First you have the initial tax abatement's which are simple subtractions.  Now these are supposed to be replace by the increased taxes based on the increased economic activity and if that actually happens we have a minor miracle.  However, to some extent, because of the pyramid nature of supply side, it creates a bubble that leads to bankruptcies, defaults, unemployment and increased Government expenditures for unemployment insurance, stimulus and reduced tax revenues.

We had a good example of this in the financial crisis where supply side applied to cheap mortgage credit led to the inevitable bubble and impacted everybody.

Now some elements of supply side have their place, especially when there is unmet demand and production capacity available.  However the precision needed to use it is generally not something Government does well.

So if we actually proceed down this path, one can ride the wave up but realize that you are definitely going to wipe out if you stay in too long.