You've convinced me to get a switch. I just ran the wiring directly to the light fixture, with a switch along the way. It works great. The light fixture isn't my favorite option, but everything is capped and snug in their boxes, and I didn't have to guess what the heck is going on in that junction box. I might change it when I become more familiar with the hodgepodge wiring in this house, but for now I'm happy with my first venture in electrical.
Thanks for your help!