This 2018 paper is quite clear [1] that, for example, immigration reduces native fertility. Yet immigration continues to be sold as the solution to ailing fertility. One can only conclude that society, or rather its rulers, at best do not care.
[1] The effect of immigration shocks on native fertility outcomes: evidence from a natural experiment - https://izajodm.springeropen.com/articles/10.1186/s40176-018...