Excuse me.
A voucher is not a subsidy. Those parents pay for education through their property taxes or through their rent. It's money taken from them and then given back to them in the form of a voucher.
Explain why conservatives should abhor giving back hard earned money.
My parents did not like the public schools where we were when I was growing up (and my mother was a teacher in that system!) so they paid for me to go to a private school. With their money. They did not expect the government to divert money to them specifically that was part of their societal obligation.