You kind of missed my point, but anyway...

That smallpox initiated by terrorism could cause widespread damage assumes:

1. that terrorists actually have access to smallpox organisms
2. that they have the capability to produce it in relatively large quantities
3. that they have the capability of "weaponizing" it
4. that they have a means of disseminating it effectively
5. that the response by health authorities would be shoddy

There are countless "what-if" nightmare scenarios, and if anyone were to try to prepare for all of them they might as well just curl up and die right now and save the trouble. Think of wassisname and the killer asteroids.