If you think that employers are contributing to SS, Medicare and FICA on illegals you certainly need to read more on the illegal immigration problem. That money is going into the pockets of the employer.
Many, thought not all, employers hire illegals who use false ID and a fake SSN. That was the case with Wal-Mart. They make all those SS, Medicare and FICA paymments not knowing the person they hired is not who they claim to be.