I think immigration is like diminishing returns.

When America was first founded, it was just 13 colonies with most of the continent being unexplored at the time. It made sense to bring in new people who could settle those new areas.

But after the 1900s, importing new people wasn't worth it. Hell, the U.S even passed laws in the 1920s that was meant to slow it down significantly.

The immigrants who arrive today, aren't going to build new roads, schools, hospitals etc. They're just here to compete against the already existing natives for the same resources. So in that effect, mass immigration is now a negative influence.