Why should the government spend money on its citizens? 

Government is mandated by the Constitution to provide for the General Welfare. It can so provide by spending money to ensure that its citizens enjoy life, liberty, and the pursuit of happiness. Financial resources can empower individuals to create the knowledge that enables them to predict and adapt to sudden catastrophic changee, thereby raising the survival fitness of the society (and forestalling its decline and fall).

One good way government can empower individuals is by providing a basic income guarantee. Each individual then has a choice whether to enter the market, or pursue their own interests. Government and private businesses can hold challenges to stimulate the native instinct for innovation that most of us are born with. Challenges are already being used: Google bug bounties, the Netflix Prize, X-Prize, challenge.gov, kaggle.com. A Basic Income would free up more individuals who so choose to enter these competitions and benefit society with disruptive innovations that the private sector alone might never invest in.

How can the government finance its spending? By creating money; or by borrowing money created by the Federal Reserve. Since the Federal Reserve refunds the interest on government bonds to the Treasury, the government's borrowing costs by this method are essentially zero.

Taxes are not necessary to fund the government. Individuals who want to contribute to funding the government can buy government bonds and receive interest, instead of being forced to give the government money.

Since government can fund itself with created and/or borrowed money, the argument "I don't want my taxes to pay for ..." is rendered invalid. If one objects to government spending on some program, one must give reasons other than "there's not enough revenue." For example: if you don't believe the government should go to war, you should provide reasons other than "we can't afford it", because we can. Instead, one might say there are better ways to accomplish the objectives of war. We can provide an example of the benefits of peace and freedom. We can use negotiation, sanctions, give money to the enemy's citizens so they will be more friendly to us, provide free uncensored internet to the target country so their citizens can express their grievances and organize amongst themselves.