You are wrong on this one. The technology for a suit case bomb exists and has for some time.
Even if it didn't, a dirty bomb with a conventional explosive could make a segment of any city un-inhabitable. It is for this reason that some of us argue for a secure border. I don't care about amnesty for illegals. I think that issue is one both sides of the aisle have created. But the idea that someone who dislikes America can make Manhatten, or another banking and commerce center uninhabitable with a few pounds of high grade radioactive material scares me a bit.
So, I'm all for screening incoming containers, and think this is not the place to focus our savings. I'm all for securing our borders, while also understanding that it is a bit like attempting to keep a full sponge from leaking water.