System wide ad blockers can’t block a lot of ads, namely same-domain ads or those that are built into the html. Much rarer than the external page kind (DNS ones) thankfully.

Libraries are ethical because they pay for the books. If we’re limited to only physical books, then they buy new ones every ~8-12 rentals. Additionally (though I couldn’t verify this through a search), I’ve heard they also pay more to buy them.