this is a bit late, but hope this helps: 1 there is a standard argument for free trade, which states it is optimal for all countries to have zero tariffs (given

this is a bit late, but hope this helps: 1 there is a standard argument for free trade, which states it is optimal for all countries to have zero tariffs (given usual conditions for such arguments). 2 there are arguments that, in certain, very special conditions, optimal for a single country to have no tariffs even if others do 3 more generally one cannot say - this is called argument of second best - and adding a tariff may make situation better not worse