What is wrong with illegal immigrants In the US?

What is wrong with illegal immigrants? Other then them being illegally over here! Like the Mexicans and stuff why do Americans make such a big deal about it? I mean most of the time the reason illegal Mexicans are over here is so they can work and send there money to there families in Mexico because an American dollar is worth more there so there juss trying to help there families! But why cant we as Americans juss be okay with them here there not really hurting anything i mean my dad works for this carpentry buisness and alot of the workers are Mexicans and they work really well!! So why does it really matter? i mean they work and there not hurting anyone!! Also why do the American Government make the mom and dad who are illegal immigrants move back to mexico but they allow the children to stay if they were born here why do they not juss let the parents stay?? Honestly why waste the time the effort and the money attempting to send all the illegal immigrants back? If all they do is sneak right back over here?? Why does it matter?? Why dont they juss leave the alone? I dont get it so does anyone have a answer?