Immigration is a hot button issue in America. Surprising, seeing as most who live on the continent can trace roots back no more than a few hundred years, if that. Even the American Indian tribes were not the first humans to live in North America. The Americas still have some of the youngest societies on the face of the Earth.
So, what causes the strong exclusionary feelings of a Nation of immigrants about allowing others to immigrate to the Nation? The answer most likely has less to do with legal or illegal and more to do with a human bias that plagues even our technologically savvy, civilized society.
Bring Us Your Poor...
That beautiful sonnet that was memorialized on the statue of liberty in the early 1900's gives an indication of how other countries viewed the land of the free and the policy on immigration. Indeed, before 1924 it was not very hard for people to enter the country with a dream and a prayer from any corner of the Earth.
Post-War Immigration Reforms
Really most issues have been post war. After each major war there has been reform primarily designed to keep the numbers of undesired races from flooding the country. Which races are undesired at the time usually depend on how the most recent war went. Allies and those with higher financial and social standing were preferred.
With this being much harder than it was, many people who come to America now come with the intention of sneaking in. The risk is worth it because either due to civil war, financial ruin, corruption or other hardship, staying in their home country is a worse fate than risking their lives for the chance of a bright future.
However, social perception in America has turned towards an attitude that immigrants both legal and illegal are selfish, lazy freeloaders. An attitude not supported by the facts at large. On a small scale, there are those both born and immigrated with a lazy attitude in America. However the kind of devotion it takes to sneak into the country and try to eek out a living without citizenship status does not fit in with the lazy and selfish perception.
The Human Equation
What is more likely the issue is human bias. A strong preference is shown for those who look like the majority of the general populace. That issue plays out all over the world. There is something about the human psyche that makes most people uncomfortable with those who look different than what they see in the mirror.
While it is true that children seem to lack this bias, social groups have been studied all over the world and as they age people tend to cluster into groups of like individuals. It does not seem to matter if they are rich or poor, light skinned or dark skinned, civilized or tribal, humans are still averse to difference and change. And without a willingness to understand this bias, it's unlikely immigration reform can accurately reflect fairness.