Denver's new voucher program has drawn 82 applicant private schools of all shapes and sizes. Some of them will be seized on by voucher opponents for their unsavory characteristics—one, for instance, considers homosexuality grounds for expulsion. They should probably just be glad those schools will be siphoning off the parents and students who'd be most likely to throw a hissy fit in the monopoly public school system when someone wanted to start a Gay-Straight alliance or an LGBT club. Every onerous practice of a voucher school is a political battle avoided in the public one. There are some strange double standards in the approval process, though: Applicant schools may not discriminate on grounds of race or religion, but sexual orientation discrimination is apparently jim-dandy. I figure if you're going to subsidize bigots, you may as well do it evenhandedly.
Addendum: A writer at the Rocky Mountain news writes to note that almost half of those 82 schools were denied participation in the program, including the school that threatened to expel gay students. Repulsive as I personally find that particular policy, this does raise the sort of concerns many in the comments had about public control of private school poilcy. The Supreme Court ruled in Zelman v Simmons-Harris that voucher programs are immunized from Establishment Clause scrutiny on the grounds that they enable "true private choice" rather than state favoritism. In other words, the constitutionality depends on parents, rather than government, making the central choices. That reasoning seems prima facie incompatible with this kind of aggressive state vetting.