"Gillard had to lie to someone after she failed to get a majority. She had promised no carbon tax and also promised to put a price on carbon which she intended to do using a trading scheme. For either she needed Greens support but they would only support a carbon tax. So she was caught in a Catch 22 situation and faced with having to break one promise or the other decided to break the no carbon tax promise as that kept the Greens onside. Dave R."
Summary - she lied to the Australian people so she could grab on to power!
Any way you spin it, she's a liar and the polls reflect this.
