It's not. National Lampoon was astonishingly sexist even when it came out; my mother bought me a couple when I was in fifth grade and I was shocked by how raunchy it was. Playboy they won't let you buy; surround the full frontal nudity with jokes and marijuana ads and apparently it's no longer pornography. Breakfast Club is three years after Porky's:
but fourteen years before American pie:
That we've now navigated to a place where we can watch Bender in Molly Ringwald's crotch and go "that ain't right" is progress and long overdue but it's also a comparatively minor transgression for the environment in which it first appeared.
I'm all about calling out the transgressions. My kid will watch Breakfast Club some day and she's gonna wonder at the unenlightened era in which it was created. But she will have figured out that it's not an anomaly; it's a piece of art worthy enough to be forgiven its flaws.