Actually, illegals are better than slaves.
You can hire an illegal for next to nothing only if and whem you need him/her - and you do not need to be responsible for feeding and housing him/her or their family.
Slaves, on the other hand, had a significant up-front cost and you were responsible for housing and feeding them whether they worked or didn't.
So, purely from a financial perspective, an illegal is far more economical.
We are paying for these criminal scumbags every day in every way.