Listen to what immigration opponents are REALLY saying.
They are NOT saying, "Bring in all the iilegals, we want businesses to exploit them". But, the businesses are hamstringed by federal rules - they aren't permitted to verify their immigration status, lest they be accused of discrimination. We want businesses to play by the rules, employing people who have a right to be in this country, at legal wages.
They are NOT saying, "We hate brown-skinned people." We are, however, concerned that the large numbers of foreigners in the US are changing the American culture - and not for the better. They are considerably less educated, more likely to be minimally fluent in English, more likely to be associated with gangs (and not your West Side Story gangs - look up MS-13 in a search - you'll be horrified). The statistics on drunken driving by illegals are - you should excuse the term - staggering.
What do I mean about culture? Let's just take one example. Both Spanish and English have a similar word - "compromise". In English, it means one side gives a little, the other side gives a little, and, in the end, they reach a point of agreement.
In Spanish, it means, if you win one time, you owe me the win next time.
Similar words, totally different expectations. Over time, it's possible that each side will come to understand the other's perspective.
But, that's not happening. Right now, the tendency in non-Native groups is to circle the wagons. To keep within that sub-culture, and not venture forth to learn the new ways. That's true in non-Hispanic groups, as well (in fact, even more pronounced). So, when girls in these families reach marriageable age, they are shipped off to the home country to meet and marry their family-selected husband. The more usual American practice of intermarrying into other cultures will NOT be tolerated.
That last fact will start to sow the seeds for destruction of the American culture. For that culture depends on blending, over time, into the culture of the rest of the country. Don't tell me that immigrant cultures have to remain distinct - in America, they won't. At least, they won't if they follow the pattern of previous immigrants.
Instead, we'll see the rise of sub-groups, who DON'T assimilate. Whose culture is defiantly different, who will become separate from America.