* Bardo attack spurs calls for *****down on militants * Draft anti-terror law being prepared for parliament * Rights groups worry about repressive measures By Patrick Markey and Tarek Amara TUNIS, April 8 (Reuters) - Soon After Islamist militants gunned down 21 foreign tourists in Tunisia's Bardo museum last month, newspaper columnists, radio hosts and politicians swiftly called for a merciless *****down to save their young democracy. In the cafes and mosques of working-class Tunis, fears are **w emerging that a campaign against militants may a spiral into repression like the old days of Tunisia's police state before the freedoms won in a 2011 revolt. Tunisia has since been held up as a model of democratic transition, the only country where an uprising during what came to be k**wn as the "Arab Spring" did **t end in large scale violence or civil war.