So, Donald Trump thinks XYZ thing about immigration.
Liberals hate it, conservatives generally agree with it. Anarchists (and I mean voluntary-anarchists, in the mold of 
But they're wrong. They're incorrectly applying the NAP.
The violation of the NAP is the government's claim to ownership over the land in the first place.
If you accept their claim as valid, then it follows that they can decide who can enter, even at arbitrary, in the same way you can decide who enters your house.
So the disagreement should be at the root of where they claim ownership (that no, George Washington sticking a flag in the ground 300 years ago doesn't somehow constitute legitimate ownership for this group of people).
With some heroic exceptions, like those of 
From the prism of accepting the state's claim to ownership over the land, you can have your opinions about Trump's policies and subjectively prefer different ones, but the only objective case you have is at the point where the US government claims the land.
After that it's essentially like installing traffic lights on the roads.
Your point of objection is when they taxed to fund the roads. After that, it follows that they (the owner of the roads) can make the rules for them. (And you actually prefer that they do, because taxing and then not making vaguely decent rules for the road would be even worse.)
Same with immigration. One central body claiming to own billions of acres of land is absurd. But it doesn't mean stripping them of the mechanism to filter access (which is naturally attached to the idea of ownership) would be better.
Voluntary World
Consider that in a voluntary society there would be some mechanism to determine who can enter.
There are different ways to visualize what a voluntary world would look like, and nobody really knows. But you wouldn't want it to be like people join your community willy nilly, with no mechanism to filter out bad apples or to select for the people who fit best.
A side-effect of the US government claiming all this land is that they have a large tax base and are using it to make lots of enemies around the world. So stripping them of the ability to filter access (going after this symptom rather than the root of where they initiate aggression) seems like an accident and really bad outcomes waiting to happen. You have to attack the root, or it's not balanced.