There are a few possible reasons.
By changing the demographics of the United States to favor minorities, Obama makes the country less 'white, European" and more beige and generic. That's supposed to make everyone more tolerant of those who are 'different.'
Only thing is, that isn't what happens. People who are 'different' band together. Cliques and gangs form. Compare a school or country with a highly diverse population to those that are uniform and you'll find that diversity begets violence. (It's not the only thing that does, and I don't mean to imply that. There's plenty of violence in Russia and Venezuela, but it's because economic problems also beget violence.)
Obama has probably also opened the borders because non-European immigrants tend to vote Democratic. (My friend from England assures me that it's actually quite difficult to immigrate to the U.S. from Europe right now.)
ON THE OTHER HAND, there is a plus to the immigration. Without the flood of immigrants, the U.S. population is declining. In a socialist economy, a declining population is disastrous. Taxes collected from young workers are what pay for government services on which American retirees depend, and America is also being flooded with new retirees right now.
That's the story. For reasons both good and bad (mostly bad), the borders are now wide open and illegals are pouring in. We'll never again be the kind of nation we once were. I *strongly* recommend moving to a rural location and doing your best to become self-sufficient. Dark times lie dead ahead.