Alp franking credit changes I want a straight answer, page-455

"So, why, if a taxpayer has a tax rate of 19c, should that not be the effective rate that he/she pays on his/hers grossed up earnings?"

Because then the original amount of company tax is not paid in full. When refunded to a zero tax recipient the company tax isn't paid at all. 

That is the fundamental principle here. And that is the fundamental principle applied in equivalent tax jurisdictions.