1. In other words you would like to have zero immigrants. You will not find any economists agreeing with you on that one. I consider the breadth of American history and immigration and figure we need immigrants the same way we need air, water, food, shelter. Only American Indians can look at USA history and say immigration at zero might have been preferable to what happened after Europeans glommed onto the place. Not sure my ancestors were all legal either. For all I know the ones came in the 1600s were traveling on false papers to dodge charges of either heresy or horse thievery. So I admit I could be somewhat biased towards seeing the merits of immigration. Illegal immigration, no. Guest worker programs, visa extensions for the felony-free documented entrants who study here or have special skills to contribute, yes, and a reasonable path to green card status for undocumented workers who have been here a long time and are law abiding. I will not blame children brought along for the ride the parents decided to risk taking. There's neither virtue nor merit in throwing Dreamers back to their country of origin. It's a vile thing to do.
2. Maybe the Dreamers would love to have remained in Mexico. They were not asked what they wanted to do when they were minors. They were taken in hand and brought here. Think back how much autonomy you had when you were a five year old. I could wander over to the next farm (at my peril if I then chose to "adopt" one of their ducklings, as I once did and got marched back home with the evidence and an offer from that farmer's wife to my mom to sell me the damn duck) but that was about my limit. The Dreamers are as "American" as I am. They worked to get their status. They're vetted. They're contributors. They're here and they belong here. Congress critters on both sides understand that.
3. If your parents illegally emigrated from here into Mexico and took you along, it would be up to Mexico to decide if you should be allowed to stay. The rest of your question there, regarding South Africa, is not really about immigration since its occupiers and colonizers were not exactly immigrants. The question in African countries of what to do about European descendants of settlers in the post colonial era is knotty and has sometimes been addressed formally in negotiations as the governments changed hands, other times, the whites have been driven out or find themselves living in precarious situations for protracted periods as assorted land reform policies arose under new governments. Yes a child should be able to live where it was born if the government agrees and that country seems like a safe place to hang out. Otherwise... the path chosen is or forced is an emigration to somewhere the parents (or a young child able to navigate in groups with others) think might be safer.
