Governors and presidents can call in the military when needed, such as airport security. Perhaps the law can further allow civilian forces can bring in military investigators and experts when issues of high-technology weaponry overwhelm the police, but that wouldn't involve arrest powers.
Furthermore, the military isn't designed to be a police force and it weakens their training to put them into that situation.
I also agree with your point. Besides not be designed as a police force, it does not operate as one either. It operates on a whole different set of principles. Heck we can't even gather a force strenght to handle what we are doing abroad. How in the name of God are we going to handle operations abroad and operations in CONUS. This is just nuts.
I have to think there is something else going on here that is making Members of Congress react this way.