Saying that it's all about immigration vs xenophobia, and nothing else, is gross oversimplification.
For starters, immigrants may take up jobs that native-born citizens also need, but there's also the issue of outsourcing. Corporations will exploit low-wage labor, and will leave areas where workers will not accept such low salaries. Look at what outsourcing has done to places like Detroit; the jobs leave, the money leaves, and infrastructure and quality of life crumbles. Yet the United States is still a lucrative market to sell goods in, so these corporations, such as car manufacturers, still sell foreign-manufactured cars in the very places they left. They make more money because they pay the foreign workers less, while the common man and woman suffer.
This is no good for us, so Trump's solution is implementing a 35% tariff on American corporations who think they can outsource and get off easy by selling these foreign-made goods. At the same time, Trump plans to reduce the business tax to 15%, giving these corporations an even better reason to come back (as well as more money to give workers good salaries). You can already see it with various companies abandoning plans to build factories in Mexico, and investing in plants in Michigan.
Ironically, Obama said this was impossible. He asked Trump what kind of magic wand he had to bring those jobs back. Well, looks like Trump's a wizard.
Actually, walls remain a very practical means of controlling movement of people. For instance, look at the results of Hungary's border wall.
And if you question whether illegal aliens bring violent crime (which, in turn, a barrier to migration would indirectly stop), look no further than Israel's border fence.
It's mostly because it was a campaign promise.
I'm guessing public opinion is about 50-50 right now.