Considering 2 million is the bare minimum in order to sustain our current GDP growth rate, I would argue 5+ million if we ever hope to achieve real growth or prosperity. You'd need to couple that or balance that with incentives for native-born women to have babies again, especially wealthier women (replace the estate tax with a per-heir inheritance tax--encourages wealthy families to have more children and break up their estates.) Equal pay and better family leave policies, promoting a living wage...these are all things that can help Americans have more babies and thus counterbalance our need for more foreigners.
Some folks (even liberals) are starting to believe in the "doom loop" theory of liberalism--as countries adopt more liberal policies, women work more and have fewer babies, thus Western democracies need to rely on immigration for growth, which leads to populism, nationalism, fascism and eventually the death of liberalism. I think that's a pretty stupid theory, all things considered, as it's just proof that even "Western" democracies are still only paying lip service to the ideal of equal work for equal pay and decent family leave, and I think it's more an indictment of the "nuclear family" than anything else.
Some folks (even liberals) are starting to believe in the "doom loop" theory of liberalism--as countries adopt more liberal policies, women work more and have fewer babies, thus Western democracies need to rely on immigration for growth, which leads to populism, nationalism, fascism and eventually the death of liberalism. I think that's a pretty stupid theory, all things considered, as it's just proof that even "Western" democracies are still only paying lip service to the ideal of equal work for equal pay and decent family leave, and I think it's more an indictment of the "nuclear family" than anything else.