Yes. Capitalism will exist so long as there is scarcity. Humanity has proven that when technology gives us abundance, we will reproduce until there's scarcity again. Machines can make things more efficient, but not faster than humans breed.
In 1980, the US was about 80% white demographically. Today it's about 63% white and falling rapidly. The difference between those two, is tens of millions of immigrants from Latin America and Asia. The US has absorbed 10 to 12 million immigrants from just Mexico since 1980.
Remove the immigration from Latin America + Asia and US population growth over the last 30 years in particular falls to barely a trickle; it'd likely be flat at this point.
Untrue; the US still has a positive rate of natural increase. Immigration is responsible for a hair more growth than natural increase, but isn't the sole source of increase.
Naturally increase in the non-native population isn't increase "due to immigration", either in the terms normally used in population dynamics, or, really, in any meaningful sense other than the way in which all population increase in a place where humanity didn't arise is attributable to some past migration.
That's entirely consistent; below replacement fertility doesn't imply a current negative rate of natural increase, though if maintained indefinitely it implies an eventual negative rate of natural increase. [1]
[0] examples: https://knoema.com/atlas/United-States-of-America/topics/Dem... http://www.prb.org/Publications/Articles/2012/us-population-... http://www.susps.org/overview/birthrates.html
[1] Assuming the replacement rate is accurate, but current replacement rates are based on projections into the future based on past mortality trends, and can be inaccurate in projecting what is needed for replacement for that reason.