Dogs need to be walked

and they need to be walked often.
I was talking to someone on my regular pedalling route yesterday - the one that gets me to the library and the shopping centre.  He is missing having a dog. His last dog died almost two years ago.
   "I'd love another dog but I couldn't walk it any more. That's not fair on a dog."
Yes, he's realistic. He walked his last dog, the one I knew, twice a day. One walk would be short, perhaps just around a couple of suburban blocks. It might be quite brisk too. But the dog knew that the other walk would be much more leisurely. Sometimes the two of them would head off in the car - just to find a new place to explore. His dog was lovely. It was well behaved, friendly without being the sort which is all over you, and alert. 
I really believe a lot of that was down to good training and all the exercise.
Next door we have a chihuahua. The owners tell me it does not need to be walked at all. It is too small for that. I don't agree. It barks a lot. It will attack people entering the property (and, for a small dog, it can do a lot of damage). It isn't trained at all. On the rare occasions it has been taken out for a walk - perhaps once every ten to twelve weeks - it is quieter and calmer.
Can dogs have mental health issues? I think they can. Like humans they need stimulation - the right sort.
Ms W's neighbours were away this last weekend. They could have put their dog in kennels but Ms W and her father cared for it instead. Their own lifestyle precludes a pet of any sort but they could manage the weekend. And off they went. They took the dog exploring on Saturday. The dog knows them well. He was a happy dog after the first hour or so.  Did he understand, "Yes, they will be back on Sunday"? I doubt it but he followed Ms W around the entire weekend. On Sunday they took him to the dog friendly park and played "frisby" and "chase the  ball". He was a very tired dog at the end of it. He slept most of the afternoon, just opened one eye when I took something in to Ms W's father. 
I've been told he was waiting at the gate when he heard his owner's car return. What would he have told his humans if he could speak?
Do people realise how much a dog needs to be walked? Cats can take themselves - even if it annoys some humans - but dogs need help to explore.