As someone who has experienced both Public and Private school educations first hand, I will affirm that is about choice and nothing else.  The choice for parents to be able to provide the best education for their children.  Vouchers create a level playing field for all parents.

When I was in the 10th grade we moved to a new state and I enrolled in the public school.  It didn't take long for my parents to realize how inferior the public schools were.  The 10th-grade curriculum covered things that I had learned in the 7th grade. My parents moved me to a private school.

Our public schools are under the influenced of teacher unions and the progressive agenda, which makes reforms difficult if not impossible.  

The reason that many Democrats and Progressives do not like school choice,  to them choice and freedom are a threat to their control.  Many on the left do not care about educational standards or educating students.  They want control to continue to push their progressive agenda,