There IS genuine concern over the safety. Those are my reasons. I don't agree with a parent refusing a vaccine that's clearly safe on religious grounds, but I respect that parent's right to raise his or her own children.
This vaccine hasn't been tested on children under 16. It's caused seizures, allergic reactions, and possibly two cases of a sometimes deadly syndrome. There have been absolutely no long term studies on this, so there's no telling if the vaccine will even last for more than 5 years or if it will give people problems later in life, like other vaccines have in the past.
It hasn't been tested extensively enough to safely make it mandatory.
If so, then why is everyone fixated on the allegedly sexual nature of this vaccine? It appears that some people are more concerned that teenagers will not get cancer from having sex, than about the supposed safety concerns.