Actually, someone in this very thread asked what problem there is that needs to be solved by the wall - implying that it is not a problem to have open borders. Others have said that controlling the borders is immoral and against the teachings of the bible because we are supposed to help those in need - again implying that we should let all these needy people in. So, actually, there are people that believe we should let them all in.
But, I'll grant that it is something of a straw man, sure, because I don't think the majority of the people are taking that stance. In any event, my point was that there are millions of people trying to get into our country and, for that reason, I believe you need controls in place to limit and restrict those numbers. Our support system, our economy, can only handle so many.
You may not believe it, but even terrible OWGs like me that want to control immigration have compassion - my heart breaks for families suffering through desperate situations around the world. I just know that, no matter how much we all would like to, we can't help them all.