First of all, the only "help" free trade needs from the gov't is low tariffs, anything else results in regulatory burdens. Secondly, if this was only about a desire to "help trade", then why the need to deny the plans for the highways? Additionally, some of us see implications regarding moving towards globalization and further compromising our national sovereignty. American trucking companies are worried about competing with the less regulated Mexican trucking companies. Land owners are worried about their land being stolen from them via eminent domain. Some are worried about providing more pores thru our borders for illegal aliens, drug dealers, and terrorists to abuse, rather than securing our borders like we should be.
If you believe that this is just about "helping trade", then I've got a bridge you might be interested in...