I’m waiting for mine to express their displeasure by softly murdering me in their sleep.
I think ‘against their will’ is the key phrase. If you have an outdoors cat and try to change things and keep it in, you’re in for trouble, and fair enough – it can’t get to its territory, it’s obviously going to be highly unhappy.
Mine have never been out, and show no interest in going out. No slipper crappage has occurred. Or any other stress behaviours. So far.
The sparrows seem OK with it as well.
I wouldn’t criticise anyone who lets their cats out. It’s a tough call. I’m just saying that the alternative, if applied properly from the start, may not be a rough option for them.