If there are UFC customers upset or otherwise dismayed at the absence of Jon Jones or Khabib Nurmagomedov from this card, they are well within their rights to do so. And if there's anything fans are entitled to do, it's act as a de facto quality control service by providing consumer feedback in the form of pay-per-view sales...or lack thereof. None of this behavior is out of bounds.
However, the UFC deserves a bit of a break here. Jones' malfeasance got him removed from the card. Nurmagomedov's aggro training forced John Makdessi to step in. Neither of these problems are not the UFC's fault.