Would more humane immigration laws in the US mean less illegal immigrants?

To answer your question: Yes. Which is why no politician will ever make it easier for immigrants to legally immigrate. Our entire economy would collapse if all the illegals here were suddenly granted citizenship. We make far, far too much money by keeping them illegal. People do not realize, for instance, that illegal immigrants pay over $7 billion a year into Social Security through means of fake SS cards that their employers - big American corporations - supply for them, requiring them to withhold that money from their paychecks, which they will never be able to collect.