The problems on our borders are immense, and our government is lying to the American People. Many believe that the political motivation behind our governments support of illegal immigration is an expectation of millions of votes for whichever political party is most supportive of the illegal immigrant ― i.e. which party grants amnesty and hands out the most government largesse to the illegals.
More accurately, this is a key part of the "Open Borders/Open Society" movement which yearns for a global governance under the "New World Order". The quickest way to accomplish globalism is to subvert nationalism by undermining the culture. The fastest way to accomplish that is to promote multiculturalism. Multiculturalism has already nearly destroyed Europe.