If your hangup is about a friend borrowing a tool, he's not really a friend. Seriously. If you can't trust him with an object that belongs to you, regardless of the value of the tool, how can you possibly call him a friend? That relationship is based on the value of a thing and not the value of a person.
I'm not looking to pick a fight, but I've seen arguments like this before and don't think I agree with them. So more just sharing my point of view.
I agree that there should be trust in friends/family and we should practice being unselfish, but I also know that many of my friends/family have "shortcomings" in a variety of ways, just like I do. Some don't have the proper training to use my table saw or chain saw, for instance (I'm don't think that tool safety is the issue in this thread, but it's a common concern). Some aren't good at taking care of tools because they never learned that concept. Some are just scatter-brained and might forget where they put something or, as in this situation, not think through the concept of something potentially getting stolen when parked at Lowes. Things going wrong/broken/stolen could put a strain on the relationship too. In some cases, you could take time to teach a friend to remove those shortcomings/concerns, but that might not solve the "right now".
None of the above makes any of those people any less of a friend or someone I love. Or someone that loves me. But I think some discernment is needed for each particular situation to figure out what makes sense. Hopefully, the situation could be discussed openly with a true friend and an agreeable solution found, maybe with some give and take on each side.
There are a number of situations for me where I'll readily go out of the way to help a friend, but I use the tool, usually because of safety concerns (I'm not talking about wrenches or hammers here, which I'll fairly readily loan out). If they're not well trained on a potentially dangerous tool, I don't want to put that risk on them.
Just my thoughts,
Tyler