To be fair, Rush was fooled by the border enforcement promises that were not kept, along with many of us. "Legalize those here already if they are worthy, and keep the rest out unless they apply and are approved" sounded fair and reasonable at the time.
Rush's immigration mantra at the time was that " ....illegal immigration was the sign of a healthy and vibrant economy ...." He and many others were deaf to the screams coming from California!
E.G., This was exactly the RINO line put out by the US Chamber of Commerce ... and dunderheads* like B-1 Bob Dornan who only woke up to the invasion when a 'Mexican' stole his job, using live, dead, and completely imaginary Mexicans, whether citizens or not! (The Amazing Loretta Sanchez Vote Fraud Story.)
After the tragic mistake of Ted Kennedy's Immigration Reform Act of 1965, the Republicans simply thought they could take advantage of it. Nixon had enjoyed very heavy support from the Cubans in Florida, and the thinkers over at the RNC thought (rather stupidly) that this meant all Hispanics would become Republicans!
Nothing wrong with Rush as a broadcaster. Bit of a mistake turning ex rock'n'roll disc jockeys into political philosophers. I'd forgive him if he admitted his mistake on this issue.
*B1 Bob was a very charming dunderhead and a strong man on defense.