Smallpox has been eradicated, that's not even virtually nonexistent.

Only risk I see is biological warfare, but why do that with a virus we have a vaccine for?

There are multiple other scenarios where the virus could become released into the wild again: infection by clearing up old storage sites, a laboratory accident, or some terrorist spending 100k US$. And all of these have happened (although the latter was "just" horse pox).

[1]: https://en.wikipedia.org/wiki/Smallpox#Post-eradication