Are we self-censoring?

If, during a supplementary school program (à la Hebrew/Religious school), one is teaching a class on the Holocaust, should parents be able to decide whether or not they want their child to participate in that class?

If yes, where is the line drawn on parents censoring what their children are learning? Should they be able to pull their child out of any class depending on its content?

Not sure where I fall on this yet. I think parents ultimately have the right to decide how they want their children to learn, but they also need to respect those that have invested thoughtful time and energy into developing curricula.

And what is it about Holocaust education specifically that generates so much anxiety?