As quoted in your lead post; all mainstream Australians should be asking that question of both sides of politics.
The GST is the largest tax ever imposed and continues to bleed people even after the end of their long working lives. It never ended all those other state taxes etc. that John Howard promised us it would.
If the mining sector can fund $25m advertising campaigns [probably subsidised via tax deductions for expenses], media shock jocks can openly push their vitriol and big players squirrel away earnings in tax havens; then mainstream Aussies have every right to hold pollies to account on matters such as taxation and expenditure.
So what does Tony Abbott have to say about how he'll fund his $80b black hole?
Why isn't our self-serving, Abbott-friendly, group-think media scrum asking that question of him?