Just set a number and anyone over the number gets sent back. If illegals are streaming over the border, then nobody in Mexico gets a visa until enough illegals are sent back to provide openings in the quota.
The INS does enforce laws in regard to LEGAL immigration. The Government does not enforce laws in regard to ILLEGAL immigration.
We deport people all the time who are here legally and who violate the terms of their legal immigration status. My daughter in law was nearly deported back to Canada because the INS misplaced one of her documents. They had no pity on her.
Yes we do deport a lot of legal immigrants. They have agreed to deportation as a penalty for violation of their immigration contract. Illegals have made no such contract. They have not agreed to be deported if they violate the terms of their visas since they have no visas. So we don't deport them.
If this sounds like Bizzaro World, it is.