I have this reoccurring fantasy that a geneticist will isolate a particular jew-gene that will be vulnerable to chemical attack.

Not such a fantasy as one might believe. Certainly jew genes have been isolated.

Article:
http://blogs.discovermagazine.com/gnxp/2009/01/how-ashkenazi-jewish-are-you/

PDF of the relevant paper:
https://genomebiology.biomedcentral.com/track/pdf/10.1186/gb-2009-10-1-r7

Current practical application:
https://www.jpost.com/Israel-News/Whos-a-Jew-Rabbinical-courts-demand-DNA-test-to-prove-Judaism-report-581989

The challenge is identifying vulnerabilities. You mentioned chemical attack. There might be other vectors as well, say with modified smallpox virus.

But of course we're just trolling and blowing smoke here. We don't really mean it. And the challenge would be impossible to solve.

The best answer to the JQ is to spread information, especially memes, and to perfect the use of good optics.

[reposted from here]