I am too excited to see this post and people's opinions about what they would do if they eventually see it. I am happy that almost everyone here sounds like a true saint that would be ready to return the BTC even though it worth upto 10 BTC. In this case I don't think many of us would ever return it even though it worth just $100. From everyone perspectives I can see that words are easier said than done.
It would really depend,
What if the private key has already been leaked or posted online?
This would be more on like a giveaway for the fastest finger. I don't think finding a private keys online would have so much $ in it even though it's a giveaway. Could that be possibility for this? No, maybe on a rare basis.
But suppose I found someone else's keys, my greed would surface, and I would definitely open them up immediately. If its value is so little and insignificant, I certainly won't need it because I'm not too poor to have to steal. But if it's a large amount of bitcoin worth millions of dollars, I don't think I'm in a hurry to return it to that person, but maybe I will take it because I think then greed will overwhelm reason.
You just explode my thought and it's good for you being sincere to yourself just like other people that are not money conscious would also react since there problem is not about taking what does not belong to them.
We are all humans and the flesh cam tempt us even though we don't have the interest to go with what does not belong to us.
If I find someone's private key and if there is a lot of money in it, then since it is not possible to trace the owner through this private key, I will distribute the funds in this wallet to poor people and donate to some organizations where orphans live.
Maybe I might be lucky to get some funds from you since you would want to be send part of it to the poor and needy.
I don't know how honest I can be then because the greed of money tries to drag everyone down the wrong path. But I will not use them in my own work until I have good knowledge
Since everyone one has some level of greed then we might be mislead by our thought to go away with the BTC but our consciousness cam drag us to give part of it out since we can not always find the owner.