Let's say few years ago I lost/forgot a photo camera in beach, and I never reported it as stolen because I lost it and it's my fault, nobody came and took it from me with a knife.
Again, irrelevant. Whether or not it is morally right to steal money which does not belong to you also does not depend whatsoever on how careful or otherwise the owner has been with that money.Finding a paper wallet, not stealing.
There is a big difference.
I don't see the difference whatsoever. Whether you find a paper wallet or whether you break in to an electronic device to access the wallet, you are stealing money which is not yours. What about if you accidentally stumble across someone's seed phrase back up? I would suspect that most people would view that as outright theft. How is that any different from stumbling across a paper wallet?There is a big difference.
If you think that any thing someone found was stolen in the world, than we are living in world that stole 99% of things and land from other people.
I mean yes, but that's beside the point.Hehe. Then Exchanges own many coins because users don't have private keys 
. They only have email and passwords.
Completely correct. If all the bitcoin you have purchased is on a centralized exchange, then you own exactly zero bitcoin. . They only have email and passwords.I will suggest you try moving the funds to another wallet
Once again, absolutely do not do this. The most likely way for the owner to access his funds is by realizing his paper wallet is lost and moving them. If you move them first, they cannot do that anymore.