A friend quoted this observation about walking behavior from reddit to me:

Walking towards somebody. The person who is walking the fastest is usually the person that makes room for the person walking slower. If you don’t feel like moving to the side when you’re walking towards somebody - slow down below their pace. Works all of the time, most of the time.

I would say that the person walking faster is responsible for not causing a collision. This could be read as the same thing, but isn’t quite: the faster person might slip through a quickly closing gap to exit the collision space, or might just walk around the slower person rather than “moving to the side” so that the slower person can pass. It applies more widely than only walking toward a facing person, too, since “don’t cause a collision” applies even if you are both walking the same way.

Also, while I understand the impulse behind slowing to avoid the responsibility of deciding where to go, in situations where one’s attention is not on the encounter, this can lead to awkwardness. I have been in multiple situations where I found myself trying to figure out why I was standing in front of someone who was looking at me expectantly or even already starting a conversation, because they thought I had stopped to talk to them, when I was just trying to be unobtrusive and slip by at a slower speed.