Anything can be illegal if the people in power want it to be illegal.
Maybe we need better laws instead of putting people into indefinite detention camps.
But good lawmaking is hard work and nobody has the will to do it.
Discussion
We simply need to enforce the laws we already have. It is illegal to just enter the country and illegal to hire them. If you break those laws you should face the consequence. Just because it has gone on so long that it has become normal for people to take advantage of our good nature doesn't mean that we can't stand up to it. Do you really think that it is reasonable that the equivalent population of entire states have been added over the past four years? Talk about getting debased.