Inside or Outside?

At the countryside in Japan like here, people usually keep their cats only outside, because when cats come into house, they scratch slide doors made of paper and wood or furniture.
Many of those people only love to feed cats, and they don't have responsibilities for them as owners, of course they never think of spay/nueter them, they often say "I don't want to spay/neuter them because they are not mine.I only give them some food."
Those situations often cause serious problems, you know, 2 or 3 cats soon would increase to 10 or 20 cats.Neighbors would call animal control offices or munincipal government and complain about that, ask officials to take cats away, but our law doesn't allow it, so animal control officials has no way to solve the problem.

I'm one of such official but I can't do anything about that as official, so I'm helping a cat rescue group and promote TNR as a volunteer.I think TNR is only way to solve these problems, but people won't believe in its effects at the beginning...That's also a problem.

Actually I keep my cats only in house and never let them to go out.It's not because it's safer for them, but my husband hate cats go out and come in with maddy foot...So he said to me when I brought the first cat from animal control center,"Don't let him go out.Our house would be muddy!"
Anyway, it's better for cats and I want also my neighbours to keep cats inside...but it's difficult to persuade them to do so, because most of people believe that cats would be happier outside.

What do you think of that? Which is happier for cats to keep outside or inside?