 Iain McMillan is the latest in a long line of prominent people to have put his head above the parapet on the issue of Scotland's constitutional future only to find himself on the receiving end of a less than gracious put-down from the ruling SNP administration.  after posing a series of questions about Scotland's future membership of the EU and the euro on behalf of the business community this week, the business leader at the Scottish CBI was summarily dismissed as "the man who has said it all before", on the basis that he also asked some hard questions in the run-up to devolution.  Chided like the schoolchild who has spent too much time gazing out of the window, he was told that he should know the answers, had he done his homework on the nationalist's White Paper Your Scotland, Your Voice.  Last week it was the turn of Lord Robertson of Port Ellen, the former Secretary-General of Nato, who was branded out of touch after he questioned the wisdom of Scotland's withdrawal.  The week before that it was the Citigroup financial giant that was accused of being ridiculous for suggesting that investment in Scottish renewables might not be wise given the constitutional uncertainty.  This strategy of playing the man not the ball is bound to succeed in deterring some business leaders and institutions from voicing their concerns about independence.  However, the only way the SNP can win an independence referendum is by carefully examining the questions posed by those sceptical of separation and addressing their fears.  alex Salmond should be wary of allowing his propaganda machine to make too many enemies in the run-up to his independence referendum. When it takes aim at Mr McMillan it's not just one former adversary that is hit but everyone else in the business community who shares his views.  The way to convince people of your argument is to engage constructively - not to question their right to enter the debate.