It is only "racist" because people are claiming it to be. The term racist and hate-speech have been used to stop any further argument or debate on a subject, primarily by the far left extremists, but not limited to. The Mexican border, as well as the Canadian border(however, not as prevalent), has to be kept in check for the sake of the negative things that come through. Can people immigrate in to our country, yes, but there are channels and avenues that must be taken. The problem is mainly with drug-trafficking, human-trafficking, and illegal immigrating, that either exacerbate these issues, or go unchecked in utilizing all of the resources available through the taxation of the real populace, while they pay none themselves. Eventually borders will be unnecessary, if humanity can somehow see all others as equal or not see others as hostile creatures. The primary problem with humans is greed and survival. Those who can't provide for themselves, take or rely on others to do it for them, and that's the current issue with the mass illegal immigration coming from Mexico and further south.
Take the somewhat unwelcome immigration in to Europe from Syria and other countries, for example. What they let in were primarily people running from war, but many others that were merely using this to infiltrate and dismantle European countries from the inside.
People who enter this country must be vetted to ensure that we aren't inviting terrorism or other hostile entities into our daily lives.