Well, your governments, be it led by democrats or conservatives, let the "so-called illegals" stay in the US for 10 - 20 years or even longer, a period where the vast majority has found roots in the communities, contributed actively to your country, had children born in the US, opened businesses, paid taxes and most of all --> does the back-breaking low-paid jobs no American ever wants to do, like cleaning your houses, cultivating your yards, picking vegetables and fruits, washing the dishes from which you ate your last burger, etc etc.
And this amid the largest police force, the most advanced surveillance programs, the largest investigative bodies etc etc. that an efficient detection and subsequent deportation shouldn't be an issue.
Fact is that you don't want and can't afford to deport them. And calling them after such a long period "illegals" is pure hypocrisy. By that definition, you could be an illegal as well, if your ancestors immigrated into the US illegally at that time, which was the norm in those days.
Hence, yes, the term "so-called illegals" is correctly used in this case.