[mildmotive]

Do you think that showing a minor pornography is okay because they can seek it out themselves?

Furthermore, do you think that buying alcohol to a minor is okay if they can seek it out themselves?

[anigbrowl]

There's a big difference between showing something to a person and that thing being available in a library whey they can seek it out or encounter it at random. You seem to be implying that library curators are leading minors to shelves and telling them to look at something they otherwise wouldn't.

[mildmotive]

They may not be actively showing this material, but at the very least they are facilitating porn use by minors. The same way as when a person offers to buy a minor alcohol, they are facilitating alcohol consumption by minors.

There is no acceptable reason to keep pornography in a school library.