I think few people forgive it. I think they just like it anyway. It’s also a young adult book that was rigidly (and heavily) marketed at a narrow age band of teen and tween girls. It’s crossover was more than half ironic in my experience.
There was certainly an amount of projection involved in the core fan base. Seeing themselves in and as the main character, that caused people to over look a lot of it’s foibles.
Similar to what I’m saying about Whedon. People wanted it to be the thing he purported it to be. And wanted to see themselves in the work. Ported that expectation over to him.
He also worked mostly in Television until around when he jumped Marvel. Where a lot of other people were involved and had a voice and contributions.
So I wonder how much of it was Whedon being adept enough to crib their genuine empathy to help gloss his creep.