My boxer is not dog friendly while on leash - especially towards other big dogs (he loves little dogs), but is fine at our local doggie day care with all sorts of dogs. The fact that they're leashed on a walk makes them feel at risk and vunerable for attack by another dog, especially one who's off leash - can't blame them really.
I usually walk Jackson at times when most other dogs are not out to avoid potential problems. I cross the street well in advance when I see another dog approaching, and I never allow an interaction to take place. Better safe than sorry, IMO.