How involved should parents be in their child's education?

New Hampshire recently passed a new law that allows parents to opt their child out of a class if they do not approve of a particular lesson being taught. As a public school teacher of Evangelical parents I can only imagine the discord that can be created from this! But -- I'm curious as to how others feel and would greatly appreciate feedback. I heard of the development through NPR this afternoon and it is further explained, here on the radio station's website.

I posted the following response on the Callie Crossley Show facebook page with other educators and parents.

I am a public school art teacher in Boston and I also teach at a private institution that is less censored than the average elementary, middle, or high school. I myself grew up with Evangelical parents who wished to have me home schooled, but I rebelled and demanded I be placed in public school. My parents, by the way, live and vote in New Hampshire.
As an artist I am against censorship of any kind, but as an educator I understand the need for regulations in public schools. That being said, I agree parents can and should teach their children whatever they wish at home, but should be less interfering in the classroom. I'm not saying uninvolved, not at all. But parents should embrace the idea that we are a society of free thinkers and that everyone is entitled to opinions or theories of their own. It's one of the many great things about this country.
Also, here in Boston the Massachusetts Comprehensive Assessment System (MCAS) is a severe concern to teachers and principals. I'm sure NH has its own test like it that measures the performance of ALL students based on curriculum framework learning standards of the state. If a parent wishes a teacher to allow a student to abstain from one lesson or another, who's to say that would not upset their chances for their highest possible score on the exam? The impact of this could bring the curve down for the entire class, grade, or even school. Sound ridiculous? Well, I can't argue with you, but it's true.
My bigger concern is that the child would be missing out on something that is the building block for something else further down his/her educational career. I like the idea of the parent being a part of the process, but I wish there was greater trust in the teacher to provide all of the necessary tools for the student.