This is like saying "adding triple redundant GPS to a self driving car is a bad idea because the GPS is the component least likely to cause you to end up at the bottom of the ocean."
There's no a priori need for password-derived key material in a library like this. To require it unilaterally is to introduce a security risk, since people have proven to be poor sources of entropy.
I don't really understand the self-driving car analogy. A better analogy would probably be three cars hitched together.
If the user enters the bottom of the ocean as their destination, it would be bad for a self-driving car to take them there. "The user is an idiot and so we killed him" is not going to be such a great defense in court...
In all seriousness, if a man puts a GLOCK 21 in his mouth and pulls the trigger, is it GLOCK that "killed him"?
If I take my car and intentionally drive into the ocean, I expect it to continue until the engine dies, and then I do shortly after. Why should machines start prohibiting me from doing stupid things, if I want to do them? I think Isaac Asimov wrote a parable about such a future.
Except this also adds very little benefit. Sure, 3 ciphers might be better than one, but as the top comment said the cipher is already the strongest part of the entire process.