Why Americans are so against Immigrants (illegal or not)?

well after reading thousands of Q and As, i hv come to the conclusion that young mexicans living here want illegals allowed, mostly because they have the same blood, which is ok, on the other hand i hv read many letters from people who went thru the proper channels of citizenship and they deplore illegals! why should the illegals be given a free ride ? yes we are all Human, and Humans no the difference between right and wrong