Social Security is also a pyramid scheme — a Ponzi scheme is a less polite term. The system only works when there is more money coming in than is being paid out.
So far this pyramid has worked because Americans were producing a lot of babies — or, to put it another way, a lot of future workers.
Americans might suddenly go crazy and again start having lots of kids. But that’s not likely given the cost of raising children nowadays. And even if there was another baby boom, that wouldn’t help for another 18 years or so when those newborns start entering the workforce.
So the only answer to keep the Social Security pyramid functioning is to allow people from other countries to come here to work, pay taxes and contribute to Social Security.