Are some airlines pocketing the taxes on non-refundable tickets?

When the airlines sell and oversell their flights, and some passengers cancel or no-show, what happens to the taxes collected on tickets? Surely, this is a subject some airlines would rather not discuss. Some airlines claim that they pay the taxes to the taxing authorities, while others decline to talk about it, or give incomplete explanations. Some airlines maintain that taxes are paid regardless, but the theory does not hold water. For example if a passenger does not travel, why should the "passenger facility charge" (PFC) be paid to the airports that did not render any "facility" to the passenger? Or why should a "security fee" be collected when the passenger did not go through security?

With hundreds of millions of dollars at stake, the airlines either have to prove payment of these taxes to the appropriate governmental entities, or they should be refunded to the passengers or their companies.