Why did Captain Smollett turn down Silver's propsal?

Smollett, disgusted with Silver's proposal, makes a counter-proposal, claiming that if the pirates come to him unarmed, he will put them in shackles and give them a fair trial. Adding insult to injury, Smollett points out that the pirates are powerless - they don't have the map and they are also on the wrong side of the island, "on a lee shore," the side that is away from the direction in which the wind blows. In conclusion, he orders Silver to leave.