"You, as a 150+ lb person, can't protect yourself from a 20-40 pound dog? Really?"
Seems like we've had this conversation before and it never sinks in.
There are more people out there than fit and nimble cyclists and joggers. Some folks on our local MUP are elderly, walking with canes. I've seen some in walkers and wheelchairs on the wider paved portions nearest the condo complexes and senior living centers.
Relative size and weight are irrelevant. A 150 lb person could easily trip over a free-range chihuahua and be seriously injured.
Dog owners are responsible for their pets. It isn't up to everyone else to be battle ready for a walk or ride in the park.