No, I understood your point. The problem was, your comment about the unreliability of the statistics presented by Tony Snow -- it was a good one -- also applies in the other direction: we can no more trust the statistics cited to show that illegal immigration is on balance "bad".
As to whether illegals "should not be here to begin with," I think it's clear that many Americans disagree, to the point that they're paying people to cross the borders. There is clearly a market for illegal immigrant labor.
The sticking point for you is the "illegal" part. Suppose, however, that a way was created for this large group of people to be here legally -- say, some sort of guest worker program that allows us to track and tax those who currently are not tracked and taxed. Would your argument about "they shouldn't be here" be addressed, or would you find some other reason to oppose their being here?
If we first truly secured the border, to the point where the flood of incoming illegals was brought down to a level that current enforcement could handle. Then if it was determined that we needed workers from other countries, then and only then would I support any new plan, law or program that allowed more people from other countries to come in to work or to live or gives legal status to those here now. And I would give priority for legal status in this country to those who are waiting in line because they are trying to follow the law, not to those here illegally.
I will not support any plan to legalize those here now or to allow more in legally until the border is secure. That is why I support a major fence/barrier on the border before any other plan is implemented. Without securing the border as step one, nothing else will work.
Illegal immigration is not the only issue that concerns me, I am concerned about the open border for other reasons also. I am deeply concerned that a terrorist could easily cross the border with little chance of getting caught. I am concerned that things such as biological weapons and dirty bombs can be smuggled in easily. I am also concerned about the border crime, including but not exclusive to drug smuggling. Illegals are only a part of the reason I want the border secured.