No? OK, we agree on that.
Now let me play a bit of devil's advocate here. What it Mary Catholic takes $5 of her welfare check and drops it in the collection basket on Sunday? Shouldn't she be excluded from receiving benefit? After all, doesn't that mean that the State™ is subsidizing her church? Isn't that a violation of Separation of church and State™?
At this point, if you're intellectually honest, you have to admit that the money, once Mary cashes her check, is controlled by Mary, and it isn't the government choosing what to do with it. If you can't follow that, then you must reverse your answer to the first question and say that all people of faith must be excluded from all government programs and entitlements.
So, if Mary "given" a tax break by the state to send her kids to private school, how is the State™ subsidizing a church? Mary can choose to use that money in any school, secular or religious. Once Mary cashes that check, it is controlled by Mary, and it isn't the government choosing what to do with it. The money itself is earmarked for education, and that's what she must spend it on, and she does.
Now, let's look at it from a purely economic perspective. Mary pays $8,000 in taxes, and her local public school costs the taxpayers $23,000 per student per year. If Mary is given an $8,000 tax break to send her kids to a different school, Mary wins, her kids win and the taxpayers win! Mar wins, because she can now afford to send her kids to the school that will educate them best. Her kids win, because they get a better education. The tax payers win, because Mary's three kids are now saving the school system $69,000 per year, for a net savings for $61,000 per year to the tax payers. [N.B. these are not made up numbers, these are actual tax rates and public school costs for a nearby town in NJ - I looked them up.]
It seems to me there is no Constitutional justification for opposing school choice, and every economic incentive to support school choice. Could it be that the real reason for opposing school choice is because legislators are in bed with big business and special interest groups?