There is a disadvantage if it turns out that these people make on average a negative contribution to the economy (i.e. if the aid they need and damage they caus

There is a disadvantage if it turns out that these people make on average a negative contribution to the economy (i.e. if the aid they need and damage they cause via crimes is higher than the surplus created by them aiding others, and producing useful labor, good and services), which would mean that they make the people already there worse off and worser off the more of them are allowed to enter. I'm not sure whether they are a positive or negative contribution, and this also depends on how good the accepting state is at integration and education.