Americans won't do certain jobs because they don't have to; thanks to a massive cradle to grave welfare system. It's where democrats get their support and soothe their conscience.
Also it is not melaninophobia, as you call it. It is the surge of tens of millions more people into a country of 320 million. Third most populous and plenty of our own problems to solve without having to solve theirs. There is no way that it won't have a detrimental effect on our opportunities and quality of life. 
America has never experienced this level of uncontrolled immigration. There were, in fact, substantial periods of no immigration in order to allow for assimilation of those who had already come.
I very much agree with you regarding their values and work ethic but we can't solve the world's problems by importing them here any more than we can go over their and force it on them. We should help them, but we should help them where they are at.
Immigration should be for the benefit of Americans.