To deport or not to deport is a red herring; consider the following:
1. Immigration has not always been illegal; using the standard of today, the only people that would be in America, for example, would be the natives.
2. Immigration is made illegal as a result of nationalism and socialism: the nationalist wants to cultivate a society which adheres to similar beliefs, naturally that of a culture which submits to the
sun god and no other sun gods, and of course immigrants coming from differing cultures "mix in" with that pool and dilute the once powerful all-hail-our-sun-god culture; whereas the socialist wants to be relieved of responsibility over his life and opts to advocate for programs and planning which help support his habit of blaming someone else for wrongdoing: the immigrant can take the freeloader's spot and eat up all the taxes to be spent on him, as many are attracted to free benefits (as, for example, many young Americans are attracted to the idea of "free college education" in other nations.) Together, they agree, as national socialists, to keep out undesirable immigration, and so setup strict border rules and ensure the only people allowed in the nation are:
A. In agreement with the culture of the nation, including language, political affiliations, and so forth, to satisfy the nationalist
B. Educated, mild-mannered (see: complacent) and productive, so as to produce lots and lots of taxes, to satisfy the socialist
3. Immigration only needs to be illegal so long as the nationalists and the socialists are appeased; without the desire to cultivate people, and without the desire to "build great works" at the public's expense, there is no need to force immigrants out (or to keep emigrants in, which is another matter entirely); the only people attracted to said nation, lacking the national socialist desires, are those who want to make a better life for themselves, thereby naturally discouraging unwanted immigration as there's nothing to freeload from and nothing to demand adherence.
That, however, would necessitate the removal of said nationalists and socialists from the accepted norm; instead, they just call themselves by different names, and continue to evade scrutiny as people aren't principled enough to see the similarity between two same things using different guises; in America's case, it's Republicans and Democrats, but they also go by the name conservative and liberal. Until that day, it doesn't really matter what you do with the illegals, whether you kick them out or keep letting them in to buy votes for your party; the fact that immigration is illegal at all is enough testament to just how fucked up people are.