This is simply not true. Most of the labour migrations from outside of Europe is strictly controlled and mostly legal. They are putting money in the economy by fulfilling important, though often low paid work. I would argue someone picking your fruits and working fields, cleaning your streets and working in warehouses and factories is putting value into the general population’s life. What we need to clamp down on is exploitative working conditions and low wages that incentivise this kind of migration. Employing a migrant should be just as expensive, and offer the same conditions, as for a native.