What was wrong about it?
What affect did it have on the USA?
Uhhh, 12-20 million illegals here - that's what it did.
I probably should expand upon that. I'll let you know what we here in the area experienced first hand from that decision. I'm in Oregon near Portland, used to be a bedroom community for an agricultural community.
Every year the pickers would arrive with the season. They'd stay at the farm provided housing or live at one of the two low rent apartment buildings built for the picker influx. Then when the season ended the INS (that's what they were called back then, the Immmigration and Naturalization Service) would drive their white vans through the complexes as a warning - season's over, time to return home. A week later they'd be back to catch and deport those who didn't get the message. Rinse, repeat.
Then the amnesty. They stayed and the schools that were once holding their own took a huge dump on the influx of students who spoke not a word of english, just like their parents (so there was no help from the household). It was very expensive and further lowered what we could offer mainstream students.
Our social services, same thing, innundated, still are today.
To cap it off, these new citizens, what was the first thing they did? Bring the family and relatives up (illegally) and the new legal citizen could shelter them and get them set up. They're still doing that. Except now, they have bought and made businesses to lengthen that support for the illegals they bring up. Bought apartment complexes and homes to shelter the folks they bring up. They know (and this is from personal contact with a good number of these folks) that if they can hold out long enough, can stay here, we'll eventually grant another amnesty, and they can start the process all over again.
ICE turns a blind eye to this.