Could there be a law on stolen bitcoins? What if there would be a law punishing those who steal bitcoins and those people behind scam sites? And if so, is it necessary to have such law? I'm just wondering, if there would be such law about stolen bitcoins, it could be a big relief to us bitcoin users. But then, there are so many questions and issues that goes with this ideal that makes me skeptical about it.

This issue differ from country to other, I think where Bitcoin is regulated, there will be a law to protect Bitcoin users, if you read Bitcoin news, you should be heard about the scammer arrested by Dubai police in UAE.
https://www.cryptocoinsnews.com/dubai-police-arrest-alleged-bitcoin-scammer-siphoned-100000-off-victims/