[xcvbxzas]

I don't think it's fair to say that development programs will just stop after a reasonable advancement on the last known state of the art.

If you (a nation) are working on this, it's fair to assume your peers are as well. If you have improved on the state of the art, it's safe to assume your peers are in a similar position or will soon be.

By making advancements, all you are doing is proving that other nations with a similar level of technical sophistication can do the same. Even if you make strong assumptions that you are indeed the best, you can't assume other nations will never reach where you are now. Maybe you have 5 years on them, because you are clearly superior? Or maybe you take a more conservative stance and assume you're behind - just in case.

Furthermore, I don't think quarantine would be an effective response to an intentional biological attack. Even just quarantining say, New York City, would be a nearly impossible task. And since this is an attack, why wouldn't all major cities be targeted? There would be no way to contain it physically.

Even if you think pure quarantine is the way to go, there is a lot of useful information that can only be gained by doing the weaponization research. What sort of incubation times could show up? How virulent, etc. Knowing these sorts of things would really improve the quarantine situation. There also isn't really a good way to know without doing the research. It doesn't mean it has to be packaged into a weapon, but the hard part is all done.