The article is mainly using a tweaked Drake equation as an poor excuse for fearmongering. The author do not really attempt to explain why biotechnology is now a threat to humanity.

Actually it has always been a threat, there are many examples like sending cadavers on catapults or kindly giving covers of people infected with smallpox. Or simply poisoning water sources, people do that since thousand of years.

It misses also another factor, which is that most terrorists do not really attempt to make as much casualties as possible. What they seems to do is attempting at making as much as possible PR in medias about them.