Imagine that the fire department decided not to put out fires at synagogues and churches. Or imagine that the police decided not to answer calls from synagogues and churches. "So sorry," they say, "there's a wall of separation around your church, and we can't cross it to help you. Hire your own fire protection and your own security guards."
This would rightly be seen as outrageous discrimination. Sure, the government shouldn't specially favor religious institutions, but the government shouldn't discriminate against them, either. The government should separate itself from religion by not caring whether a person or institution is religious -- by treating everyone equally regardless of their religious affiliation.
The same is true of education, which is for many people the most valuable benefit that the state provides. The government shouldn't give more benefits to religious school students than it gives to students at secular schools, whether government-run or private. But why must it give anything less?
The First Amendment doesn't require such discrimination against religion; it simply bars laws "respecting an establishment of religion." Equal treatment of everyone, without regard to religion, is not an establishment of religion. This is why the GI Bill, which let soldiers choose either a religious education or a secular one, was perfectly constitutional. It's why the government may give scholarships or student loans to all students, whether they're going to UCLA or Notre Dame. Equality isn't "establishment." And school choice is just a GI Bill for our nation's children.
There's no "mixing of church and state" in any of these examples. The police, the fire department, and the agencies that pay for students' education keep themselves separate from religion by remaining completely unconcerned about the school's religiosity. The government treats the religious school exactly like it treats a nonreligious institution. Both separation and equality are thus scrupulously maintained.
Are religious schools helped when the government uses my tax money to provide remedial education on the school's premises? Sure they are -- just like they're helped when the government clears the snow on the street in front of the schools, or protects them against crime, or collects their trash, or gives all flood victims, including the schools, disaster relief funds. But we accept these programs because they provide important public benefits to everyone, religious or not. Public spending for school choice should stand on the same footing: So long as the government doesn't specially favor religion, none of us has any constitutional grounds for complaint.
Some people argue that, in effect, school choice programs are pro-religious because most of their funds end up being spent at religious schools. But this is like saying that putting out a fire at a church is pro-religious because the firefighters are helping only the church. If you look at education as a whole, or firefighting as a whole, you'll find that the lion's share of all money goes to nonreligious institutions -- in education, to government-run schools. School choice programs merely mean that instead of the money going only to government-run schools, it goes to all schools, including a relatively few religious ones.
What about the fact that school choice scholarships might indirectly go to the propagation of religious views? Well, the same thing happens when government employees or welfare recipients donate part of their income to a religious institution. The same thing happens when a blind student chooses to use vocational training funds to become a minister -- something the Supreme Court unanimously held constitutional in the Witters case (1986). So long as the government gives no preference for religion, it doesn't matter where a paycheck or a welfare check or a scholarship ends up.
The government may, if it wants to, fund only government-run schools, just like it could have set up the GI Bill to cover only government-run universities. But if the voters think that it's good to give parents (or veterans) educational choice -- the power to choose a government-run school, a private secular school, or a private religious school -- that's no problem. The voters can decide to help all children, without discriminating against those whose parents choose a religious education.
My parents sent me to secular schools. If I have children, I'll probably send them to secular schools, too. But I know others have a different preference. They pay their taxes just like I do. The government may provide services for these people's kids on the same terms as it provides services for my kids.
That's the true meaning of the Constitution, whether we're talking about police services, the fire department, the GI Bill, or elementary schools. Equality for all. Special benefits for none. Discrimination against none.