That's not how it works. If you actually read up on the laws, in order to hire somebody, the employer has to obtain either proof of citizenship in the form of a US passport, or proof of lawful residence in the form of a work visa AND a driver's license or DHS/INS card.
A SS# is NOT proof enough, and any employer that does not collect the documents I mention above is breaking the law too.
Look it up.
Actually, I defy you to break the speed limit in my neck of the woods. Most of the time the traffic is so bad that you're lucky if you're doing 45...
Now seriously, coming into this country illegally is far from being in the same ballpark as breaking the speed limit. It requires a level of premeditation and effort, and causes a damage that are both far beyond going 10 miles over the speed limit.
I'd compare it to a DUI... And I'd be more than happy to deport anybody that has a DUI "incident".
Uh? So, if a law is stupid and/or nobody is enforcing it, it's OK to break it? Do you REALLY believe that?
There is more than enough technology today to find them. It's just a question of actually mining the IRS data, and enforcing employment requirements that already exist.
You really believe that sending back home people that knowingly entered this country illegally is "inhumane"? We're not talking about giving them life sentences you know... We're talking about sending them back where they came from! Why is that so bad? If Mexico is such a shithole, whose fault is that? Ours?
Remember that people that left their countries because they were being victims of persecution can easily obtain political asylum. If sending people back to poverty is THAT inhumane, how about fixing it (poverty) here first rather than keep importing other people's problems?
So I return your question: how do you identify those? How do you prevent from giving citizenship to people that are here just to send all their money back home and leave as soon as they have enough? Remember that even if you eliminated dual citizenship (which, by the way, will never happen) they can easily go back home at any time and, with their Mexican birth certificates, regain Mexican citizenship and take all their money with them.
Two wrongs don't make a right!
This country NEEDS immigrants and we should do their best to welcome them. We should make obtaining a Green Card an easier, faster and more transparent process. However, it is absurd to try to solve the problem by benefiting those who came here illegally AT THE EXPENSE of the ones that came here legally!
Look: if the amnesty proposal included ALL LEGAL immigrants too -- everybody that was here legally would also be allowed an automatic path to citizenship (rather than being sent back home after their work visa expires, which happens after 6 or 7 years depending on the work visa) -- I wouldn't be 10% as upset. In fact, I'd even be willing to support such an amnesty, for the benefit of the legal immigrants, that are being sent home for no good reason. But one that puts illegals in an advantaged position in comparison to legal immigrants? NO WAY!