You will probably get as many different responses as there are posters on here! I have an exceptionally content indoor only cat, and her brother was too. They were adopted with the condition that they were kept indoors, and turned out that Boycat had issues that meant he was a LOT safer indoors than out (probable brain damage through an accident as a kitten)
We are waiting to see if Tobias is going to be happy as an indoor cat, he had a very bad time as a stray before the rescue got him so hopefully he will be OK with it and it was a requirement of the rescue. When I've gone to get cats, I've always asked for cats who need to be indoor only due to my own anxieties.
There seems to be 2 main attitudes in different countries about cats. On one hand places like Australia and the US cats seem to be indoors by default, whereas most Mediterranean countries they roam anywhere & everywhere. The UK seems to be somewhere in the middle, and moving slowly more towards indoors only.
Cats who have been raised as indoor only tend to be content to stay that way, and obviously there are cats who can't really be allowed to roam due to health issues e.g. FiV, Boycat's mental issues & lack of self preservation, many physically disabled cats. You do need to bear in mind that indoor only cats need more enrichment provided in their homes e.g. climbing places, toys, being played with etc.
In my ideal world, I would have a catio or a highly secure garden so a middle ground, but finances and the layout of my house/garden don't permit that sadly.