On the virus he's actually writing about and the "gain of function studies" that caused so much controversy, part of the risk is not terrorists, or bad guys, or any ill intent whatsoever.
This kind of research is conducted in BSL-3 labs, and there's a not insignificant number of laboratory accidents, accidental exposures, etc. in those labs, by well-intentioned, well trained people.
I saw a presentation recently that estimated, using fairly conservative numbers, that 10 labs working on those viruses for 10 years had ~1600 deaths in expectation. Now that distribution isn't normal - lots of zeros and then some rare but catastrophic outcomes, but like many things, it doesn't require anyone to do anything actively malign. Just screw up.
This kind of research is conducted in BSL-3 labs, and there's a not insignificant number of laboratory accidents, accidental exposures, etc. in those labs, by well-intentioned, well trained people.
I saw a presentation recently that estimated, using fairly conservative numbers, that 10 labs working on those viruses for 10 years had ~1600 deaths in expectation. Now that distribution isn't normal - lots of zeros and then some rare but catastrophic outcomes, but like many things, it doesn't require anyone to do anything actively malign. Just screw up.