Not very if indeed they are kept in cages. The stupidity comes into play when you attempt to feed, med, or handle a large snake without someone else present.
My father worked at the National Zoo as a police officer and when on the night shift his favorite place to nap on break was in the reptile house amongst the venomous snakes. Which of course were in cages. Had he decide to let them out then he would have been stupid.
As for domestication of snakes I have to agree that is not going to happen simply I feel due to the size of the brain and thought process. Not much to work with there but instincts.