Should we be surprised? The people that support amnesty and open borders in general are the people and groups that stand to gain financially and numerically. Open borders -- particularly from Latin America -- will put more rear ends in the pughs during Catholic mass across the country.
Special interests support open borders in the same way that crony capitalism works -- a small group of highly-motivated, connected, campaign-contributing businesses lobbies for policy and law that directly benefits their company/organization's interests to the detriment of the mostly disconnected, disinterested population at large. In other words the politicians can pass somethIng that will greatly please their campaign contributing brethern while the masses hardly know or care how this will detrimentally impact their lives. Win - win for the politician.
In this case the open borders speciial interests get cheap compliant labor and larger numbers for their cause while the population at large gets reduced wages, disappearing jobs, and higher taxes to pay for the costs of the mostly uneducated, low-skilled immigrants