and it may be that trump's executive order will do more harm than good. i would guess so.
on the other hand, as a person born to a country with salt-water frontiers on all sides, i think control of one's borders is a useful thing. so i am not opposed in principle to policies which strengthen them.
i have wondered myself for a while if global travel could survive international terrorism. the european experiment seems to suggest it is currently a naive ideal. every network generates viruses. to combat viruses you need an immune system.