Well, maybe it IS jealousy on my part, but yes, I have known great horses that the owners didn't ride or spend time with and thought "what a waste."
I think it goes back to my childhood when I wanted a horse more than anything else in the world. And now I have horses and STILL feel that way. So if I see a nice horse that is rideable and the owners don't use it, yes, I do think "what a waste" because someone like me could really be enjoying that horse.
I do sort of think that if someone isn't going to ride them anyway and just wants a horse to decorate a pasture (and that IS a great life for a horse!) why not pick a horse that is old or lame and deserves a good home? It would be a win-win for the horse and owner. You are giving a horse that may not otherwise find a home a chance at a great life.
I DO think there is a downside to not using a perfectly healthy horse and letting it "sit." What if you had to sell that horse? Not even for money but just because you couldn't care for it anymore? It will have a lot less chance of finding a good home if it's only job in years has been "pasture puff." There are a ton of those out there. Any horse can accomplish that. But a horse that is usable and doesn't require remedial training because he's been pasture puffing for the last 10 years, he will be more likely to get a good home, don't you think?
If you were in the market for a horse, which would you buy (or even take for free)? The pasture puff that never does anything (and who knows if he's even trained) or the horse that has been ridden regularly a couple times a week? Which one is ready-to-ride and which one may or may not be spoiled and need more training? The ridden horse is more of a sure thing. You know what you have. The pasture puff, well, he may or may not be a useful animal. He will be harder to find a home for.
Now I don't feel you have to ride to enjoy horses. Of course not. And horses LOVE the life of pasture puff. But you may be putting his future in jeopardy if you have to re-home him and his biggest claim to fame is eating grass.
(donning flame suit)