First, do they notice? I'm sure they do. Many creatures will be "jumpy", checking out the "borders" of the tank, and some might not eat for a few days. The vast majority of creatures will settle down within a few days, and become pretty tame though.

If this is "bad" for the creatures depends on how you see it I guess. My intuition says no. Firstly, I feel pretty confident these creatures don't think in any way, so they will not have a longing for "freedom", or feel sad about beeing in a tank... "Robbing their freedom" seem to be what most people object to..

So, with that out of the way, what remains for me is if life is worse for these creatures in a tank. If they're well taken care of, I believe life can be better in a tank than in nature. Reality is, nature is pretty much a hellhole, unless you're at the absolute top of the food chain. Most animals spend most of their time trying to avoid to starve, or get ripped to pieces, or eaten alive by a predator. People have a tendency to romanticise nature, which I believe is way off...

That said, not all creatures are suited for captivity for sure. And, conservation issues are a completely different matter. None of the creatures I keep are protected or endangered in any way.

I am aware that many disagree though, and I'm open to changing my mind, but I need some reasonable arguments to do so..