As the war on drugs has also demonstrated, there is only but so much behavior-shaping you can achieve with people via the law.

If a law is consistently and chronicallhy broken (and especially if the harm for breaking said law is minimal), at some point one must ask if the law is too incompatible with human behavior to justify enforcement or existence.

I don't think anyone "soft on illegal immigration" is against legal immigration. But they may very well be against the laws as they currently stand, because the laws are demonstrably shaped by racist intent; the national quota system used to decide people per year from each country where very much structured out of fear of a "browning" of America.