The probability of the CDC's stock escaping is really very small, and let's face it, if we got rid of it once we could get rid of it again.
Contrast this with polio, where there are about a thousand infections per every paralysis. Thanks to a couple of ignorant leaders who claimed that the polio vaccine is a Western conspiracy to sterilize African girls, it's spreading again. Great.
a) It has no animal reservoirs
b) The latent period of infection is very short
c) There's an effective vaccine
None of those things would be different the second time around, unless the viruses itself was changed.
It's worth noting that the US has a gigantic stockpile of smallpox vaccine already - and they're actually increasing the size of the stockpile because of worries about bioterrorism (in 2010 20 million doses of an updated and safer vaccine were added to the stockpile[1]). The vaccine is made with cowpox, so smallpox samples are not required for its production.
http://www.usatoday.com/news/health/2010-05-25-smallpox25_ST...
If there was an outbreak, couldn't we quickly isolate the virus and have our stocks back?
What is the probability of the virus escaping from the labs in Georgia and Siberia? What is the probability that there are undeclared stocks of the virus elsewhere? If the second is greater than the first, don't destroy the stocks because you may need them to recreate the vaccine. If the second is less than the first, by how much? And what is the consensus on risk appetite? How well can you ensure that the stocks really are destroyed if they are so ordered to be?
This should tell you the best answer based on safety.
The next set of questions relate to what can be learned from the current stocks. Is there an active research program? Is there a current list of things to learn, or are we just holding onto it 'in case'? Has there been a case that we were glad to have virus stocks that were previously held to be useless?
If there is no obvious gain from holding onto the stock for research and the most significant threat from the virus is accidental release, then destroy the stocks. Otherwise, hold onto them - you can't recreate the stocks from nothing yet and you can always destroy them later.
My gut tells me that we should hold onto them. I'm always loathe to throw opportunities away and that's really what these stocks represent.