The first time terrorists pop a nuke, the government will have to do something. Armies and massive police forces ought to be able to smash large organized groups. The first time a disgruntled postal worker pops a nuke, it's too late for everybody. The power achieved cannot be taken back. The choices are universal surveillance, mind control, or physical danger.
Cheap nukes are only a for-instance.
One person can already do hefty damage, and the trend is always up. People are willing to give up civil liberties for safety from serious crime, and the more damage one person can do, the fewer criminals it takes to make crime serious. But the point is, freedom in the future is an iffy thing. We need to stay on our toes.