>I would tell them jQuery isn't available in this job. Half would immediately drop out. Good.

Unless the job description made clear why it wasn't available, I would take this as a sign of a toxic workplace and avoid it. It isn't about jQuery being banned, it is about the type of workplace where jQuery is not only banned, but such a ban is mentioned early in the interview process. I guess if you want people who are okay with such a workplace, then you are using an appropriate heuristic.