Longtime journalist Jon East explains why.
It's no secret why the defenders of the monopoly system, both nationally and in Oklahoma, use the word "voucher." They believe it to be a dirty word, and thus useful for demonization purposes. I don't think they realize that Oklahomans actually favor vouchers by a wide margin (survey methodology here). Given the popularity of vouchers, I cheerfully encourage voucher friends and foes alike to use the V word liberally.
But we shouldn't use the word voucher when we're talking about tax-credit scholarships.