Because first, the law under which Perry issued his order didn't have an "opt-in" process, it had an "opt-out" process, like all school-required vaccine laws.
And second, because a vaccine law with an "opt-in" makes absolutely NO SENSE. If you want to take a vaccine, you can take it, you don't need permission. So a law that said "you are required to take this vaccine for school, except you don't have to, and but if you want to, go right ahead" would be a useless law. You wouldn't have to send a note to school to GET the vaccine, and you wouldn't have to send ANY note to school saying you TOOK the vaccine, so the law would have absolutely no effect.
What I guess we really needed was a DIFFERENT law, that provided a set of vaccines that were NOT required, but for which the school vaccine policies would apply IF the parents chose to get the vaccine. That way, the vaccine would be on the insurance coverage, and the reduced-free vaccine program for poor people would cover it.
Except some here have complained about tax dollars being used in a way that would encourage sexual activity, so I'm not sure having such a law would be acceptable to them. And since every parent could skip the Gardisil vaccine by simply going online and saying "no", it doesn't really look like the opponents are REALLY fighting over it being "mandatory".
Essentially, I think you make very good points and believe we are fairly much in agreement with one another.
Sorry I did cause that confusion by forgetting to italicize the other poster's "opt-in" question. I think I have received more replies on that post than any other post I have done since I joined FR in 1998!