Why does Solanio think the Duke will forgive the forfeiture? Why doesn’t Antonio?

Solanio believes the Duke would never allow such a barbaric act against a Christian by a Jew to take place, "I am sure the duke
Will never grant this forfeiture to hold." Antonio believes that the Duke must uphold contracts and the law because not doing so would threaten security of all foreign merchants in Venice and ruin the city's business reputation, 

"The duke cannot deny the course of law.
For the commodity that strangers have
With us in Venice, if it be denied,
Will much impeach the justice of his state,
Since that the trade and profit of the city
Consisteth of all nations."