On our course they teach us that really the majority of cats would be far happier kept alone. People get a second cat to keep the other one company but unless they are family they never really like each other. Like you say cats really are solitary. But then I'm sure lots of people would say actually their non related cats get on great and seem to enjoy each others companyMany (currently, wild) cats are solitary though, or at least semi solitary, I don't like seeing cats locked in 24/7 either I do lock my cat in at night, my fault I raised her around dogs and she has no fear of them at all and will merrily go up and rub all over them, and we have lots of foxes out behind the house and they will kill cats especially very small friendly ones.
This is a really good thread, lots of thought evoking bits to it