Nicola Roxon has announced that she will not stand at the next election, thus she's been given the customary opportunity to make a valedictory, a final speech.    Ms Roxon spoke about sexism, "it really is time for people to understand how corrosive sexism is".    I can think of perhaps a more corrosive influence in our polity - corruption.   Cover-up and denial of wrong doing in the face of overwhelming evidence is now worn as a badge of honour amongst some - as if the "strength" of staring down accusers rather than owning up is a virtue.