Interesting SWP piece (in German) on causes of migration

See SWP’s publication here

Whilst there is a correlation between poor countries getting richer, and higher migration (when you are dirt poor, you cannot pay for a rogue to transport you), they list multiple other factors that shape migration, e.g: demographic change with more youth, structural economic change with rural to urban drift, inequality, access to credit, number of others already having emigrated, and how severe the barriers to immigration are in the richer countries. The conclusions is: “do not throw the baby out with bathwater” (helping countries grow is a good thing, even if it may increase propensity to migrate), and we should have a regulated official migration system that undermines the people trafficers (offering a cheaper legal option to the dangerous expensive one).

But the admission ist made: the more severe the barriers set to illegal entry (or over-stay in) rich countries  – confirmed en passant in The Economist – the less the attraction of migration. So how then to be ruthless on illegals, without pushing those already in the country underground (with all the risks that this poses of unreported crime etc)?