I await the opprobrium to be aimed in my direction.
I don't care how well trained a dog is, it remains an unpredictable wild animal at heart and you can never be sure what it will do and how it will react to a variety of stimuli. If around other people, and especially on a relatively confined shared space such as a canal towpath or shared footpath a dog should always, without exception, be on a short lead. Likewise on any sort of road, including footpaths and bridleways.
If training was all encompassing then police dog handlers wouldn't bother keeping their dogs on leads, but they do, just in case.
To be fair, I don't usually have a problem with dogs, but often enough, I do, usually in the confined path situation.