This is easily explained. The government does not produce anything. Everything the government purchases or uses requires taking money from the private sector in order to pay for it. Think of the government as a symbiotic parasite on the people. It is necessary to a point, but the bigger the government gets the bigger demand it has on its host, ie the people. The bigger the demand the less the people can contribute to their own needs and desires ultimately hobbling the economy and its ability to grow now and in the future, Economists don't even rank taxes with added value to the economy, but as transfer payments moving money from one area of the economy(the private sector) to another(the government sector) having no effect on the economy's growth. Even if the government borrows money it has to pay it back later with interest, so the effect on the economy is actually negative because the government has to withdraw more money from the private sector than it added during the borrowing in order to pay the money back.