They may have done so originally, but it is evident that at the time they didn't see how this would adversely affect them in the future. They didn't count on the North getting such strong control over congress (Did you notice that the "Free Soil Party" was headquartered in New York?) that they wouldn't be able to change them later. They also didn't realize what would be the negative consequences to them of the "Navigation act of 1817". (Which I don't want to get into right now.)