I used to think that, but after owning quite a few animals...not so much. One of my current dogs seems more anxious and depressed that any dog I've ever owned or met. I've blamed that on myself (because I'm depressed and anxious myself and am afraid I turned my dog into the same thing), but at the same time I give her so much love, and obviously a food and roof. I've met people that treat their dogs in pretty upsetting ways too, and yet their dogs were very happy. The dogs I've known that seemed depressed are few, but I don't think it's right to say all dogs would be happy with love, food, and a roof. In my experiences, that just isnt true. Dogs are as different from each other as people are from one another, and I think that also comes in forms of happiness and sadness. Not that I'm comparing human happiness and sadness to dogs at all though, because, yes, on a whole I'm pretty sure no other animal has the level of self-loathing many humans do, and many dogs ARE incredible with the abuse they take and happiness that returns to them when they are rescued by someone.