Seems like it would be easier to keep them out at the border than police all employment. Either way, I'd rather they just stick with the cheap labor and let they states decide whether they want to bankrupt themselves with welfare.
Also, illegal border crossing is a serious health safety and welfare issue that is completely ignored in all of this. Which favors border security.
it seems way easier to police employment. all you need is a decent id system and penalties for flouting the law. way less costly and causes way less distortion than trying to stop anyone from crossing a two thousand mile long invisible line. not to mention that currently (with the allegedly unsecured, horribly porous border), something like 40% of illegals arrive legally and overstay their visas.
illegally crossing the border is a health and welfare issue because in order to cross a border that we attempt to secure, people pay violent, amoral criminals to smuggle them across and/or attempt to cross in areas that have inhospitable, dangerous climates and terrains. stop trying to secure the border and that all immediately goes away.