Absolutely. Many drugs targeting one disease have been found to cure others. The list includes cancer drugs, antibiotics, antiviral compounds, etc. And that's just drugs, what about the research itself, isn't it obvious it has implications well beyond any one single thing. And isn't that the case for every kind of research, not just medical? To me this seems obvious.
All we need for disaster is one person who's intelligent, driven, and wants to destroy the human race.
Again, we already have that, it's called mother nature. HIV, Ebola, 1918 flu, current flu, etc, all natural.
Here's where I see the problem with your argument, it assumes great asymmetry.
Here's what I mean by asymmetry, I think you imply that if we have the technology to create super viruses on demand that does not mean we'll have anywhere near equivalent knowledge and technology to fight them.
I happen to consider that an extraordinary claim. To me the symmetry of knowledge is self evident. Almost as soon as we invent the nuclear bomb, we also invest nuclear power. Almost as soon as we can gene splice, we have gene therapy for humans which has already been successful applied.
If we have the ability to create super viruses on demand, then we also have the ability to create drugs for them, to detect them, to stop transmission, and most obviously to create vaccines for them. If you can manufacture the virus, it would be one hell of a cosmic improbability that you are also NOT able to manufacture a vaccine for it.
Alternatively if we don't have the knowledge to make viruses and vaccines on demand, that won't stop mother nature from her never ending quest to kills us all.