Okay, it's not like I wasn't warned that this was a weedy plant, when I decided to let one grow in the back yard. And it's not like I hadn't, at one point, counted up the number of seeds in a single pod, and then the number of pods on a single stem, and then the number of stems on the whole plant, and did the math. I had ample opportunities to turn back, to (literally) nip the whole thing in the bud, and I didn't take them.
It's not all bad; they do pull up fairly easily, especially when the ground is wet. The less-pleasant part is how there are thousands of them, with tens of thousands more in the soil, waiting to germinate later. So yeah, probably a mistake.