Can green cards be taken away?

Yes. For any number of reasons. Getting it back is done via the INS/Federal Court system. The best option would be to consult an attorney who specializes in Immigration law.

A further point of law..............If your documents are "taken away from you" by the U.S. Government, you are now ILLEGAL in the USA and are subject to being deported by the INS. In other Words you are heading home.

>>>>>> YES!!!!!! Most people think that once they have a green card they are home free, ABSOLUTELY NOT. And at that point, you are officially ILLEGAL, but you can go to immigration court to appeal whatever it is that made you have you have your Green card revoked in the first place(violent crimes, sex offenses, crimes of moral turpitude, fradulent marriages, abandoning your residency by staying out of the US too long, etc)