You may do well by taking a look at some statistics on poverty in the US. There’s a significant chunk of the population who can keep a book dry but don’t have $200 to just sink into this imaginary library deposit. The interest is irrelevant, you’re asking them to choose between “get books” and “buy food”. All to solve a problem that doesn’t exist.
I was in the middle of typing out a response, but looking at your parallel comments, the fact that you outright just don’t think people living in poverty are worthy of using a public service suggests this root node has bottomed out.
It's not that, but rather, this thread has basically been steered by various individuals into revolving purely around this issue of some extremely poor not being able to put up a deposit. I'm not interested in that angle at all; the idea isn't conceived to keep those people from borrowing from the perspective that they are specifically a problem (which they are not). People who can put up the deposit cause problems; it is designed for them, not as a wall against those who cannot.
It takes little imagination to see that the scheme could be shaped in ways to accommodate the very poor. E.g. there doesn't have to be a minimum deposit of $200; a substantially lower deposit like $20 or $10 could some borrowing privileges. Book or two, not twelve kind a thing. Plus any number of other mitigating solutions.
Memberships would not require a deposit. Like to log in to an Internet terminal with your library ID would not require one. Lost library cards could be free as well.
Needless to say, this would be completely ridiculous outside of America. If I think about libraries in, hmm, Austria or Japan doing anything this, I just have shake my head, no.
There is a broad population segment in America that has no respect though.
