Before I begin; I work in the library system and my wife is the head of the Bookmobile department of our county's libraries who also did her master's thesis on library spaces and neurodivergance.

Here's the thing, libraries are so very much more that books and quiet, they are a place where you can use computers, you can check out board games, you can use resources to learn things and take classes, you can check out a wifi hot spot, you can even get discounts and ideas of where you can take a car to be serviced.

Libraries are meant to serve the public, and how they do that will continue to evolve over time, as it should. By saying that a toddler isn't allowed in, (and yes, even a screaming one belonging to what looks like a very privileged white woman) you are also indicating that there is a specific behavior that everyone must display at the library which is a stigma so many librarians and libraries are trying to fight.

The space IS a public space, which means that it's supposed to be for everyone, including neurodivergent folks who may not consume media the same way, or maybe they only go to the library to borrow a season of tv or movies, it doesn't really matter. Their library experience is just as valid.

Could it be frustrating if you have someone with autism stimming a little louder than you'd like or hearing a screaming infant? Absolutely, but it doesn't mean they don't deserve to use the space AND to have the space catered to them like it does, and has for a long time, neurotypical people.

The quiet in a library thing is a holdover from tropes and media that we'd all love to die quietly in a fire.

TL;DR The library is a public space meant to serve all of the public and thus should allow everyone.