Strangers? No. Never.
I would never lend a knife to anyone if I did not know their level of personal responsibility, maturity, and knowledge of how to safely handle a knife.
Handing over a sharp knife to a complete stranger to do whatever they want to do seems like a really bad idea to me.
And even if it appears obvious what they intend to do with it, once you hand it over and it's in their possession, THEY have control of it, and are free to do whatever they want with it. After all, what are you going to do if you see them start doing something stupid, dangerous, or potentially destructive with your knife? Are you going to grab a sharp knife out of someones hand?
I don't carry an extra knife to lend out to people. Just like I don't carry an extra cell phone to lend out. If people cannot be bothered to carry their own knife, I'm not going to carry one around for them. Nor am I going to maintain a "loaner" knife and keep it sharp just to lend it out to others so they can possibly ruin the edge, and then I have to fix it.
Here's an interesting little story about lending a knife to a stranger- As a teenager, a friend of mine was fishing off a pier. There was another teen fishing nearby. This other teen asked my friend if he could borrow his knife. My friend, being a nice guy, handed over his knife. After the guy cut what he wanted to cut, he said to my friend "Thanks for the knife", closed the knife, and put it in his pocket. He STOLE my friends knife. And what could my friend do? There were no cops around. And even if there had been, my friend had no way to prove it was his knife. It would be his word against the other guys. And my friend wasn't a tough guy, he wasn't going to fight the guy to try and get his knife back.
The moral of that story is- Not everybody in this world is an honest, trustworthy, upstanding person. And sometimes when you lend out your stuff, you may not get it back. My friend was minus one knife, but he had learned a valuable lesson.
What would you do if you lent your knife (perhaps a nice knife) to a total stranger, and they decided to keep it? Could you prove that it's yours? There are certainly lots of unethical people in this world. And you can't tell who they are just by looking at them.