I have a paved yard. I try to train my dogs as much as possible to only go in our yard, but if we're out for hours/the day and they need to go they can hardly ask me to take them to a public toilet, can they?
Dogs on a decent diet/not ill should do small, firm stools that don't smell too bad and don't leave skid marks. BARF is great for this. However when my dogs are ill or I get a foster in who's got a dicky tummy I know how many hours, bottles of bleach, buckets of boiling water and scrubbing brushes it takes to keep my yard clean. Expecting dog owners to do this on walks is unrealistic.
Dogs can be trained to go on command, but if they're out and about and need to go, they need to go and they can't always tell you, of course if you know your dog well enough, you know when they're thinking of going and can move them somewhere appropriate, if possible. Pooing in the gutter is not safe for the dogs or motorists and Barbra Woodhouse, fortunately, is mostly discredited by those upto date on canine training and behavior.
Dogs aren't the only animals who poo in the great outdoors, there's foxes, badgers, birds, cats, mice, rats, voles etc. etc. etc. No-one goes around follwing them with buckets of bleach and scrubbing brushes do they?
The world is not sterile and nor should it be.
The lady picked up the bulk of the mess. That is all she could have done. YABU and slightly hysterical. I find that people make more mess than animals anyway. Dog shit will eventually wash away, wrappers, cans and plastic bags won't.