"most psychopaths are incompetent"

I wish you were right.

Psychopaths have a wide range of traits, but I believe those who would consider doing something like this, also tend to have poor impulse control that may interfere with their plans ahead. What makes it a terrifying possibility is that terrorists, who I don't think are all psychopathic, may have a better chance of pulling it off.

Not to mention that the vast majority of people who would be willing and capable of pulling off such an attack are probably people in government, so government regulation wouldn't make sense as a recommendation.