Your reasoning on guns was correct. Remember how almost every year we worry about what kind of influenza we'll get? We all worry about a repeat of the 1918 flu, which is quite likely on any given year.
Remember how antibiotic resistance keeps getting worse and worse (or better and better from the bacteria's perspective)?
HIV originated in nature, probably somewhere not too far from where Ebola is natural brewing now.
Our number one threat is mother nature. Her and other humans living close to domestic and wild animals around the world and air lines.
At any given time we might have to cope with an 1918 like flu.
Custom tailoring a virus to include one people but not other is going to be extremely hard. We are all very closely related. Human conflict tends to be between neighbors, and for example the people most genetically similar to the Israelis are the Palestinians. So the probability of a custom tailored virus is far, far, FAR lower than the probability of a natural don't-give-a-crap-who-it-kills virus.
it seems that Ashkenazi jews are quite distinct from Palestinians. there might be a small overlap between the groups(upper right corner), but a terrorist could still target a specific subgroup of the ashkenazi jews. and using more principal components might get him a better separation between the groups.
Additionally, cures by their nature will always lag behind diseases, people won't invest resources curing a disease that doesn't exist. A non-trivial amount of damage would occur before society reacted to the threat.
Also, it's not illogical for there to be a demand for (research into) protections against threats which have not materialized yet, but seem to have a chance of doing so. As the prospect of portable bioweapons becomes more likely, there will be increased incentive to come up with protections from those weapons, even if they have not yet reached viability.