I've had cats all my life, and they sit on their asses doing nothing for most of the day. They sleep...
I don't think anyone suggested it was cruel. Just not ideal for a lot of cats. Have a look at my post. Plenty of cats who prefer to stay indoors.
I also think anyone is being unreasonable. Cat's are free roaming animals. Most of them enjoy the outdoors. If you want an indoor cat, then no one is knocking it or saying it is bad. Some people don't have the time to take care of an indoor cat who requires extra stimualtion and litter changes (since you mentioned that).
Plenty of people differ in their opinions on how to raise animals. For example, I wouldn't keep a german shepard in an urban flat. I wouldn't say that those who do are cruel.
Rats are a great option and misunderstood and intelligent creatures. :)