[summer]

The cynical side of me thinks that there are some "conservatives" who merely want a government entitlement to a private school education for their children...

I think there are many people who would agree with you on that one. So long as these vouchers remain in the hands of the poor, low income, disabled, or for failing schools only, then, your claim is a tougher sell. But, if the whole system drastically changes, you might suddenly find a lot more people oppose it.

[Trailerpark Badass]

So long as these vouchers remain in the hands of the poor, low income, disabled, or for failing schools only, then, your claim is a tougher sell

Hardly, since those recipients are precisely the ones, through their advocates, who would oppose the creation of tax credits for private secondary education.