The immigrants fill those jobs for lower wages, and if they are illegal the employer can usually save on social security contributions as well. By increasing the supply of work at lower cost, the immigrants hurt the domestic workers, but if the immigrants were not there not all their jobs would be filled: each worker would be more costly and so fewer would be hired. So, if you had as many illegal immigrants as unemployed citizens, removing the immigrants would not reduce the unemployment to zero. Far from it, actually.

guaranteed to evoke a violent reaction from police is to challenge their right to "define the situation." --- David Graeber citing Marc Cooper