"If it's productive to go around killing terrorists to prevent terrorism then shouldn't we also be concentrating some of our efforts on cleaning up these sloppy stockpiles? "

We have been doing this for several years. One problem is the Russians are aiding Iran in their nuclear program- which kicks in a US law prohibting aid to Russia- which btw is also interfering with NASA working with Russian space program. The point isn't that we aren't doing this, but rather it's a question of, are we putting enough attention and resources towards it- we spending billions and getting fairly good results, so if we spend tens billions the "logic" is we get there quicker and have better results.