How often does this happen though and is it really an issue in the overall scheme of things... Even if it happens 10 thousand times a years (which is probably a way high estimate) so? That nothing.
These aren't gang members and drug dealers doing this, its mother desperate for a better life. How will probab;y work their asses off and be good people.
There's always going to be loopholes and people side steping laws. The question is, is this really a hill worth dying on? And causing a MANY other bigger issues to try and fix?
100 thousand years of biological drive and evolution? Add on culture and religious drive to reproduce.
One of the earliest ways religions attempted (and still do) become the dominant religion was simply out breeding the other ones.