You have to look at what the GST is spent on.
A 15% GST in 2015-16 fiscal year would generate around an extra $28 Billion nationally.
source:This $28 billion would be redistributed almost entirely into public services but public services also spend vast sums on private suppliers and will need more govt employees to provide the extra public services.
Income tax cuts combined with a boost in State Govt expenditures should generate additional economic activity and more employment with it which generates more income tax and company tax revenues for the Federal Govt.
What opponents to the regressive nature of the GST dismiss is the FACT that taxation benefits low income earners the most.
Most of the Scandinavian social democracies have high levels of VAT (which is just a GST by another name). These States (Finland for example) have comparable marginal income tax rates, much lower company tax rates
and a VAT of 25%
They also have low cost quality universal health care and university education.
Labor and Leftists just use the GST as a political wedge. Keating got another term by howling down the GST in just this fashion. Shorten is beating the same drum.
State Public servant unions should champion the GST and shout its virtues from the highest mountain.
In the last 8 years GST revenues have averaged about $48 billion p.a..
source: Had the GST been at 15% an extra $24 billion dollars every year could have been channeled into State Government public services.
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More money, means more jobs and better conditions for State Govt employees which is what the state public services unions should be supporting.
I can see why Labor State Premiers are taking a liking to having it increased......