I don't know of anyone on TH recommending tariffs, that is typically union backed talked to make pricing more competitive (i.e. "level the playing field"...what kind of talk does that sound like). As to stemming immigration, this relates to ILLEGAL IMMIGRATION. No one is trying to kick out folks that are engineers or doctors that come for advanced education and want to stay, it's the mass of unskilled folks that come and have babies that end up on welfare (i.e. non-productive folks) that U.S. citizens aren't real happy about.
As to "Opportunity Costs".....see above sentence about welfare to support future generations that are resultant from illegal immigration. You can also file Solyndra under that.