Whatever the rhetoric from the left and refugee advocates, the electoral reality is fairly simple. There is a substantial group of voters -- in April, more than a quarter -- who still think the current government's policy on asylum seekers is too soft. Another 34% think the current policy is appropriate. Twenty-two per cent of people think the current policy is too tough. But less than a third of that 22% are Labor voters. Even assuming all of them shift to the Greens on boat turnbacks -- highly unlikely -- their preferences will flow back to Labor anyway, except perhaps in a couple of inner-city seats where MPs like Anthony Albanese -- Shorten's rival for the leadership of the party in 2013 -- are.
But the flipside of losing votes to the Greens is that more than a quarter of Labor voters think the current policy is too soft. Ruling out boat turnbacks has nearly as much potential to lose votes as embracing them -- except the "too soft" votes, once lost, won't flow back to Labor via preferences, because they'll go to the Coalition. In short, the argument that Labor will lose votes embracing turnbacks doesn't stand up.