In the summer of 2015, during his first presidential run, the 76-year-old senator even pinned the policy of open borders on the other side of the aisle.
“That’s a right-wing proposal, which says essentially there is no United States,” Sanders told Vox at the time. “It would make everybody in America poorer. You’re doing away with the concept of a nation state, and I don’t think there’s any country in the world that believes in that.”
“Bring in all kinds of people, work for $2 or $3 an hour, that would be great for them,” he continued. [Source]
I'm positive Bernie Sanders looks forward to the day when nation-state borders disappear.
When he says right-wing, he means laissez-faire capitalists. Not all right-wingers are that. When he says "that would be great for them," he means those laissez-faire capitalists. Laissez-faire means anarchist. So, he's talking about capitalists who oppose government, the state, democracy, etc. They want only the capitalists marketplace to decide everything. Of course, that would lead to one person sitting atop the financial and economic pyramid of the entire world: a totalitarian dictator to whom all would be beholden.
The Austrian School of Economics (libertarian) openly stated their opposition to democracy. Imagine having no vote but with the dollars in your wallet and bank accounts. Who'd control even more than they already do? How long would it be before we'd undergo an extremely bloody revolution to free the economic slaves?
Some anarcho-capitalists qualify the position by saying that the only government that would exist would be the courts of the anarcho-capitalists. Those courts supposedly would protect the little fish from the big ones. I find the concept ludicrous. Who'd enforce it? Who'd own the most firepower and have the most money to employ the largest army?
You simply aren't going to bring heaven to Earth via tempered dog-eat-dog. You are only going to bring it via giving and sharing within the purest form of democracy you can create. It's call consensus building. Without building toward cooperation rather than competition as the incentive, you simply can't bring the highest and best obtainable. This is a well-established fact in psychology, sociology, fact-based rather than ideologically driven economics, and even theology, if you will.
The way to end up with viable open borders is by helping nation-states right where they are. That takes cooperation, not simply opening capitalist markets within those nations. Laissez-faire comes with no rules. There are no inherent environmental standards. That's why we have the environmental catastrophe we have. There are no labor standards. There are no health standards. There are no safety standards. It's a free for all: chaos that never sorts itself out because it kills itself off (humanity) before the "markets" can change. Greed outraces sense.