When is it wrong to keep a solitary pet

I always think of animals from my point of view that if I was in a cage all day alone what would I feel. I think that belief was reinforced when I saw that cartoon "Happy Feet" where they kept him and several penguins in a "display room" for visitors to the zoo and it was like they were slowly being driven mad. I only have cats and dogs. My dog gets walked by different family members 3 times a day since I want to be sure she is able to socialize with other dogs. We also have a big yard for her, the neighbors dogs and the cats to play in.