You raised a couple of good points that also came up in court.
First, you suggested that there must be a distinction between government spending and private parties that invite individual tax credits, and it sounds like that's something that Arizona tried to argue, to which Justice Kagan responded:
SCOTUSblog wrote:Kagan shortly picked up on that line of questioning, suggesting that if a state could not constitutionally give a tuition voucher only to a student going to a Catholic school, “why is the state allowed to use intermediaries to do” the same?
This, to me, is a pretty incisive question: if the State invites you to give your money (specifically the money you would otherwise pay to the government in taxes for the government to go and spend in the way that it will) to a private tuition organization that discriminates, is that really all that different from the State subsidizing those private organizations?
Your second point was similar to one that the Justices raised: if tax credits really are just government money in a different lights, what does that mean for other kinds of money? Now, you took it further and asked if all money was government's because it makes it, but I'd say the fact that it distributes the money means that it's not the government money.
The reason a tax credit is the government's money, it is argued, is that the government has the power to levy taxes, and it's only through that taxes that the government imposes a debt on its citizens. But rather than collect on the taxpayer's debt, a tax credit allows some of the debt to be discharged to a third party. Here's how the lawyer (a Phoenix tax law professor) explained it to some of the more skeptical justices:
SCOTUSblog wrote:The lawyer said that the money that is involved in the Arizona program is money raised by a tax; without a tax, there would be no tax credit.
Justice Alito then wondered if he would say the same about a tax deduction; the question, and similar questions by other Justices, would give Bender a chance to explain further. He said there is a difference between a deduction and a credit. Under a tax deduction scheme, he said, that is money that a taxpayer never owes or pays to the government; the choice of where those particular dollars go is made by the taxpayer, not the government. After the money is gone, the government allows a deduction on it.
By contrast, the lawyer said, a taxpayer who owes the government a tax obligation cannot keep that money or give it away to anyone or spend it on anything else but the tax bill. Under the Arizona program, he continued, a taxpayer fills out a tax return, knows what money he owes the government, then transfers some of those dollars, through the credit, to a tuition organization that decides who gets a scholarship funded by the credit. That, he insisted, is what makes it a “government spending” program.