I generally agree with this, but there is more nuance involved- like what if the library has a sign that says "Keep out"? Does the trespasser then bear some responsibility? i.e. Being served a 403, then appending some URL param that grants access. I wouldn't call this hacking, but it's something else- like "Digital trespassing", after all the 403 is a sign, not a cop. All of this to say The Simpsons did it.