Dogs are everywhere. If one percent of them makes trouble it guarantees my encouter with one sooner or later. I would have nothing against some dog running beside me for less than a minute but theres the uncertainty. Before you can judge the situation you are already exposed to the risk of being bitten no matter how small.
The civility around other peoples animals goes straight out of the window if some dog begins to make small bites against my foot. If some random bicyclist feels threathened because of a dog I might say the problem is almost always caused by the dog and its owner.
Spraying an agressive dog with pepper spray might upset the dog owner. In my experience most of the owners of annoying dogs seem always to think there is never nothing wrong with their pet or they are just incapable in some other way.