I wanted to give peaceful co-existence a chance, so first I tried flicking them off. But it turns out they are a very mean-spirited bunch and used my "walk softly" approach against me. If you drive them off one plant, they attack another. That is the nature of flea beetles.
Yet it turns out that even biological controls are subject to the Peter Principle. They are effective up to a point, but eventually they meet their match. In my case, their match was the flea beetle.
The pyrethrin worked. The flea beetles are (mostly) gone. All that's left are an inferiority complex and a guilty conscience. Nice going.