I haven't heard her stance before, but it seems interesting and I agree with what I've read so far.
With that in mind, I do support an open border. Why wouldn't you? A closed border denies freedom of movement under arbitrary restrictions of "productivity" (or random lottery, which is just as arbitrary), aka you only earn the freedom to move if you've been deemed productive -- so people with physical disabilities preventing them from working, or severe mental illness should be denied the right to move where they wish? Or that person from the Congo shouldn't be allowed to come here simply as a circumstance of their birth?
I'm sure almost everyone on HN would decry the Berlin Wall as a authoritarian human rights abuse. And lets be clear, most western nations aren't shooting people trying to cross the border on sight, and usually have some sort of asylum process (that may take years and years, however). But the limitation of movement itself is also a human rights abuse, in my mind. German families were cut off from each other, unable to see relatives trapped on the other side of the wall. The Stasi secret police were able to apprehend and torture people unable to escape because of the wall -- a closed border makes authoritarian regimes more powerful. The US is far from East Germany, but why even begin down that path? Don't we supposedly value freedom above all else? Didn't Franklin say "He who would sacrifice freedom for a little temporary safety deserves neither"? How is a closed border compatible with that sentiment?
Westerners didn't ask permission to invade the Congo, or India, or hundreds of other places in the global south, and we certainly didn't get visas before stripping those countries of natural resources and their cultural heritage (see: every item in the British Museum that they refuse to return), and then we turn around and say hey you can't come here without our permission? How hypocritical is that?
And lets not kid ourselves that closed borders keeps "the bad people" out -- people who want to commit crimes generally don't care about following immigration laws. They'll dig tunnels under walls, pilot submarines full of cocaine past the Coast Guard (this really happens), and extort desperate people trying to escape violence and crushing poverty.
So yes, I do think a closed border is immoral. If it means more strain on welfare programs in the short run as people try to start new lives here, well, if we can afford trillions to bomb the middle east into the stone age, we can probably afford that.