If books are lent to someone trustworthy and who you know and trust will return the book, there should be no problem. But if you lend the book to someone who you know tries to keep things for themselves, steals or loses things easily, than no, you shouldn`t lend them a book (particularly one you enjoy reading/like.)
I really only allow my close friends to borrow my books, but I'm still apprehensive about letting even my close friends borrow them. My books are like my children, and I love them a lot. Like, it's a problem. I think that many book lovers can relate to this topic when a friend asks to borrow a book. We don't want to, but we do it anyways out of kindness. And of course, this does not go for everyone. Some people think that books are meant to be shared amongst everyone. And I support this, except for the fact that I actually like and enjoy organizing my books so they look all nice and pretty. (And as I've said before, I have a serious problem).
But in the past, I have let people borrow my books and take them home. As a result of this, my books have gotten water damaged, the pages have been ripped and torn, and I've even gotten food crumbs within the pages. I'm sorry, but those types of things have totally eliminated my trust to let people borrow my books. And this is why I'm so apprehensive to let people take them, even my close friends. And yes, I am aware that not everyone acts like that, (Godzilla tearing my books apart), but I'm just really really worried that the same thing will happen again.
I think lending out books are okay, but the owner has to know and learn to be okay with the fact that their books might get damaged. Some people don't care about the book itself, when others do.