As I understand it the Mount Gambier passengers tax increase (which Rex could and should pass on to passengers) is to put some money into the kitty for runway works (nothing major done since the runway was constructed in WWII) - sound planning one would think.
The Port Lincoln situation is different - the route is robust enough to have two carriers. Passenger numbers have increased since Qlink re-entered the market (seriously this time). I predicted that Rex would reduce their flight schedule by up to three flights per days and that is was has happened. Passengers now have a choice and the standard fare reduced from $107 to around $90 one way. Qlink with Qantas have the ability to grow the market with discount through-fares to other capital city ports and locals and visitors alike are taking advantage of that. More tourists are visiting and increasing that sector of Port Lincoln's economy. Rex are the only ones to be feeling the pinch - it's called a free market economy and Mr Lodge blaming the locals for putting air services into a downward spiral by choosing to fly on the alternative to Rex is just sour grapes.