Because it is socialist to suggest that government spending is more efficient and produces more economic activity than does spending by individuals and businesses. It is absurd because it is an idea whose enactment has repeatedly failed ever since Engels brought it up. Do you need a list of failed socialist experiments? What is the motivation for efficiency when you are spending someone else's resources? Capacity you did not earn? Ear mark that.
I never said government spending is more efficient. I've said it's necessary. I can't cover everything without writing a textbook, so stop putting words into my mouth. I was talking about stimulus, and even waste can create stimulus.
RGS made a salient point (atypical for him, I might add) about spending to meet a budget. This does not happen in small business, but it happens in many goverenment agencies and big corporations, which tend to be bureaucratic. I believe we need to eliminate the perverse incentives that RGS described, but that is another textbook.
Some economic activities produce stimulus, e.g. purchasing a car. Other activities, such as transferring funds from one investment to a similar investment, produce little or none. Different activities produce different levels of stimulus.
Tax cuts for the poor and working class go almost completely into activities that stimulate the economy. But tax cuts have been concentrated to benefit the wealthy, who put a large chunk of it into activities that generate meager or no economic stimulus. When you compare the net simulative effect of the tax cuts, you begin to understand why the economy falters when the supply-siders say it will soar.
Supply side economics is a hoax. It is the economic equivalent of a fad diet. People who will reap millions in savings are selling it to the rest of us for their own gain. We get a few hundred dollars in illusory savings, while every man, woman and child winds up owing almost $30,000 each on our national debt, and annual interest of roughly $1,000 each.