I was confused by those posts and want to have a double check with you on this.
As what you says that it's illegal for any companies to offer illegal immigrants the job but they work to pay the tax... ? It means that it's legal for illegal immigrants to have the job in your country because of pay the tax?
Illegal immigrants here in Germany work in private households to earn money... or support from their families and friends, etc or work at black markets. They cannot get job without residence permit. They even don't have any medical care, education, school, etc.
I have mixed feeling after read those link... 
Illegal Immigrants in Germany: No Work, School or Medical Care
Illegal Immigrants in Germany: No Work, School or Medical Care - JOURNAL CHRETIEN
