They did in 1986.
"required employers to attest to their employees' immigration status;
made it illegal to hire or recruit illegal immigrants knowingly;
legalized certain seasonal agricultural undocumented immigrants, and;
legalized undocumented immigrants who entered the United States before January 1, 1982 and had resided there continuously with the penalty of a fine, back taxes due, and admission of guilt; candidates were required to prove that they were not guilty of crimes, that they were in the country before January 1, 1982, and that they possessed at least a minimal knowledge about U.S. history, government, and the English language."
First of all, no one (at least none of the conservatives I know) is against legal immigration.
That said, why haven't the above stipulations been enforced over the last 30 years when both parties have had power?
Now that we have a president who wants to address the situation (it was one of the things he ran on), you leftists start
screaming racism, discrimination and inhumanity. Who's drinking the "Kool-aid"?