"If you increase the tax burden on businesses and wealthy individuals too much they will just leave the country entirely."
When there are profits to be made, businesses will come and stay. If business A does not want to stay because of "high taxation", there will always be business B, or C, or D which are ready to fill the void. The greed factors will make sure of that.
There are reasons other than taxation why people choose to make Australia their home. Are we taxing the wealthy individuals "too much" ? I don't think so. Using effective tax planning, these wealthy individuals are already not paying the official tax rates.
