But everybody who has said "it's just a bin" - it's not "just a bin" is it? Where is this bin to go? In the middle of the library? That would put the library users off for sure. In the toilet? But then, as someone pointed out, the implication is that you change your baby's nappy in the toilet - and how can you, if there is no changing table. So if you provide a bin, the expectation is that you will be providing 'a place' to change a nappy - ie., proper facilities. This means you need a room big enough to accommodate a changing table/fold down changing table, somewhere to wash hands, etc.
So "a bin" as a solution is a little naive, I think.
The library I mostly worked in was a very old, listed building - it did have a public toilet (just one, not separate for men and women) and we had to keep it permanently locked as otherwise we would find used syringes and occasionally ODd drug users collapsed on the floor. There was not enough room in there for even a nappy bin, let alone a changing table.
If we'd had a nappy bin, it would have had to be elsewhere - behind the counter maybe..mmmm.
When someone needed to change their child's nappy they did so, usually on their own changing mat in the children's section - and sometimes, yes, we would find the discarded nappy in one of the wastepaper bins later (you get very good at following your nose when you work in a library).
So do I think nappy changing facilities should be provided? Yes - in an ideal world there would be a purpose built room with a large changing table, hand washing facilities, proper disposal and one of those automatic air fresherners that goes "phisssh" every few minutes. Never going to happen unless all libraries are privatised, though and that's a depressing thought.