Nativists Can’t Predict the Future

Many anti-immigrationists display a remarkable confidence in their ability to forecast how immigrants will act for many years into the future. So, for example, the nativists often allege that if, say, Mexicans are permitted to enter the USA, they will sooner or later vote for governmental measures to plunder the current residents and redistribute the loot to themselves. What gives the nativists such powers of divining the future, especially when they have no special knowledge of social science or ethnic history?