[DoodleDawg]

The southern states initially supported it, but came to regret it because it effectively handed a monopoly to northern shipping interests.

If there was no interest in establishing a ship-building industry or creating costal packet lines in the south to begin with then why would they complain if the North filled the gap?

[DiogenesLamp]

Northern shipping companies had the mail carrying contract. This gave them a bottom line of profitability that could not be matched by any other company which did not have such contracts.