According to the New Scientist, a US government funded scientist developed a extra deadly mouse virus, simlar to small pox, that kill mouse also if they were vaccinated and taking drugs. There might be a medical upside to research like this, but the potential danger in such discoveries is much larger. The next white powder envelopes might take out New York.
In general, I'm all for research. People want to know stuff, you can't stop them. But this is rather specific. It is not like trying to find out what atoms are made of and discover a new and very efficient way of killing a hundred thousand people a shot. Designing a killer virus is something doctor Evil in would do in a bad comic book.
There are enough killer diseases out there already. We don't need new & improved ones.